In setting a smtp relay server, adding a virtual host domain will cause an error.


CentOS 6.10

Virtualmin GPL

I am trying to build an smtp relay server using postfix on one linux box.

I confirmed that the virtual host domain was added well.

I changed some settings to set the smtp relay server.

In the current state, the email relay works well, but adding the virtual host domain causes the following error.

Failed to create virtual server: No virtual domains file (virtual_alias_maps) was found in your Postfix configuration!

So I added the following line to /etc/postfix/ to add the virtual host domain, and I get the following error in smtp relay.

virtual_alias_maps = hash:/etc/postfix/virtual

… sending failed: SMTP command rcpt to: failed: 550 5.1.1 Recipient address rejected: User unknown in virtual alias table, line 5.

Anyone, please resolve this issue.

Thank you.

below is /etc/postfix/

myhostname = mail.(
mydomain = (
myorigin = $mydomain

home_mailbox = mail/

home_mailbox = Maildir/
mynetworks =, (my webserver IP)
inet_interfaces = all
inet_protocols = all
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
smtpd_sasl_type = dovecot
smtpd_sasl_path = private/auth
smtpd_sasl_local_domain =
smtpd_sasl_security_options = noanonymous
broken_sasl_auth_clients = yes
smtpd_sasl_auth_enable = yes
smtpd_recipient_restrictions = permit_sasl_authenticated,permit_mynetworks,reject_unauth_destination
smtp_tls_security_level = may
smtpd_tls_security_level = may
smtp_tls_note_starttls_offer = yes
smtpd_tls_loglevel = 1
smtpd_tls_key_file = /etc/postfix/ssl/server.key
smtpd_tls_cert_file = /etc/postfix/ssl/server.crt
smtpd_tls_received_header = yes
smtpd_tls_session_cache_timeout = 3600s
tls_random_source = dev:/dev/urandom

virtual_alias_maps = hash:/etc/postfix/virtual

below is /etc/postfix/

Postfix master process configuration file. For details on the format

of the file, see the master(5) manual page (command: “man 5 master”).

Do not forget to execute “postfix reload” after editing this file.


service type private unpriv chroot wakeup maxproc command + args

(yes) (yes) (yes) (never) (100)


smtp inet n - n - - smtpd
#smtp inet n - n - 1 postscreen
#smtpd pass - - n - - smtpd
#dnsblog unix - - n - 0 dnsblog
#tlsproxy unix - - n - 0 tlsproxy
submission inet n - n - - smtpd
-o syslog_name=postfix/submission
-o smtpd_tls_security_level=encrypt
-o smtpd_sasl_auth_enable=yes
-o smtpd_reject_unlisted_recipient=no

-o smtpd_client_restrictions=$mua_client_restrictions

-o smtpd_helo_restrictions=$mua_helo_restrictions

-o smtpd_sender_restrictions=$mua_sender_restrictions

-o smtpd_recipient_restrictions=permit_sasl_authenticated,reject
-o milter_macro_daemon_name=ORIGINATING
smtps inet n - n - - smtpd
-o syslog_name=postfix/smtps
-o smtpd_tls_wrappermode=yes
-o smtpd_sasl_auth_enable=yes
-o smtpd_reject_unlisted_recipient=no

-o smtpd_client_restrictions=$mua_client_restrictions

-o smtpd_helo_restrictions=$mua_helo_restrictions

-o smtpd_sender_restrictions=$mua_sender_restrictions

#628 inet n - n - - qmqpd
pickup fifo n - n 60 1 pickup
cleanup unix n - n - 0 cleanup
qmgr fifo n - n 300 1 qmgr
#qmgr fifo n - n 300 1 oqmgr
tlsmgr unix - - n 1000? 1 tlsmgr
rewrite unix - - n - - trivial-rewrite
bounce unix - - n - 0 bounce
defer unix - - n - 0 bounce
trace unix - - n - 0 bounce
verify unix - - n - 1 verify
flush unix n - n 1000? 0 flush
proxymap unix - - n - - proxymap
proxywrite unix - - n - 1 proxymap
smtp unix - - n - - smtp

When relaying mail as backup MX, disable fallback_relay to avoid MX loops

relay unix - - n - - smtp
-o smtp_fallback_relay=

-o smtp_helo_timeout=5 -o smtp_connect_timeout=5

showq unix n - n - - showq
error unix - - n - - error
retry unix - - n - - error
discard unix - - n - - discard
local unix - n n - - local
virtual unix - n n - - virtual
lmtp unix - - n - - lmtp
anvil unix - - n - 1 anvil
scache unix - - n - 1 scache


Interfaces to non-Postfix software. Be sure to examine the manual

pages of the non-Postfix software to find out what options it wants.

Many of the following services use the Postfix pipe(8) delivery

agent. See the pipe(8) man page for information about ${recipient}

and other message envelope options.


maildrop. See the Postfix MAILDROP_README file for details.

Also specify in maildrop_destination_recipient_limit=1

#maildrop unix - n n - - pipe

flags=DRhu user=vmail argv=/usr/local/bin/maildrop -d ${recipient}


The Cyrus deliver program has changed incompatibly, multiple times.

#old-cyrus unix - n n - - pipe

flags=R user=cyrus argv=/usr/lib/cyrus-imapd/deliver -e -m ${extension} ${user}


Cyrus 2.1.5 (Amos Gouaux)

Also specify in cyrus_destination_recipient_limit=1

#cyrus unix - n n - - pipe

user=cyrus argv=/usr/lib/cyrus-imapd/deliver -e -r ${sender} -m ${extension} ${user}


See the Postfix UUCP_README file for configuration details.

#uucp unix - n n - - pipe

flags=Fqhu user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)


Other external delivery methods.

#ifmail unix - n n - - pipe

flags=F user=ftn argv=/usr/lib/ifmail/ifmail -r $nexthop ($recipient)

#bsmtp unix - n n - - pipe

flags=Fq. user=bsmtp argv=/usr/local/sbin/bsmtp -f $sender $nexthop $recipient

#scalemail-backend unix - n n - 2 pipe

flags=R user=scalemail argv=/usr/lib/scalemail/bin/scalemail-store

${nexthop} ${user} ${extension}

#mailman unix - n n - - pipe

flags=FR user=list argv=/usr/lib/mailman/bin/

${nexthop} ${user}

submission inet n - n - - smtpd -o smtpd_sasl_auth_enable=yes

below is /etc/dovecot/conf.d/10-mail.conf

Mailbox locations and namespaces

Location for users’ mailboxes. The default is empty, which means that Dovecot

tries to find the mailboxes automatically. This won’t work if the user

doesn’t yet have any mail, so you should explicitly tell Dovecot the full


If you’re using mbox, giving a path to the INBOX file (eg. /var/mail/%u)

isn’t enough. You’ll also need to tell Dovecot where the other mmespaces ailboxes are

kept. This is called the “root mail directory”, and it must be the first

path given in the mail_location setting.

There are a few special variables you can use, eg.:

%u - username

%n - user part in user@domain, same as %u if there’s no domain

%d - domain part in user@domain, empty if there’s no domain

%h - home directory

See doc/wiki/Variables.txt for full list. Some examples:

mail_location = maildir:~/Maildir

mail_location = mbox:~/mail:INBOX=/var/mail/%u

mail_location = mbox:/var/mail/%d/%1n/%n:INDEX=/var/indexes/%d/%1n/%n


#mail_location =
mail_location = maildir:~/Maildir:INDEX=/var/lib/dovecot-virtualmin/index/%u:CONTROL=/var/lib/dovecot-virtualmin/control/%u

If you need to set multiple mailbox locations or want to change default

namespace settings, you can do it by defining namespace sections.

You can have private, shared and public namespaces. Private namespaces

are for user’s personal mails. Shared namespaces are for accessing other

users’ mmespaces ailboxes that have been shared. Public namespaces are for shared

mailboxes that are managed by sysadmin. If you create any shared or public

namespaces you’ll typically want to enable ACL plugin also, otherwise all

users can access all the shared mailboxes, assuming they have permissions

on filesystem level to do so.

REMEMBER: If you add any namespaces, the default namespace must be added

explicitly, ie. mail_location does nothing unless you have a namespace

without a location setting. Default namespace is simply done by having a

namespace with empty prefix.

#namespace {

Namespace type: private, shared or public

#type = private

Hierarchy separator to use. You should use the same separator for all

namespaces or some clients get confused. ‘/’ is usually a good one.

The default however depends on the underlying mail storage format.

#separator =

Prefix required to access this namespace. This needs to be different for

all namespaces. For example “Public/”.

#prefix =

Physical location of the mailbox. This is in same format as

mail_location, which is also the default for it.

#location =

There can be only one INBOX, and this setting defines which namespace

has it.

#inbox = no

If namespace is hidden, it’s not advertised to clients via NAMESPACE

extension. You’ll most likely also want to set list=no. This is mostly

useful when converting from another server with different namespaces which

you want to deprecate but still keep working. For example you can create

hidden namespaces with prefixes “~/mail/”, “~%u/mail/” and “mail/”.

#hidden = no

Show the mailboxes under this namespace with LIST command. This makes the

namespace visible for clients that don’t support NAMESPACE extension.

“children” value lists child mailboxes, but hides the namespace prefix.

#list = yes

Namespace handles its own subscriptions. If set to “no”, the parent

namespace handles them (empty prefix should always have this as “yes”)

#subscriptions = yes

Example shared namespace configuration

#namespace {
#type = shared
#separator = /

Mailboxes are visible under “shared/user@domain/”

%%n, %%d and %%u are expanded to the destination user.

#prefix = shared/%%u/

Mail location for other users’ mailboxes. Note that %variables and ~/

expands to the logged in user’s data. %%n, %%d, %%u and %%h expand to the

destination user’s data.

#location = maildir:%%h/Maildir:INDEX=~/Maildir/shared/%%u

Use the default namespace for saving subscriptions.

#subscriptions = no

List the shared/ namespace only if there are visible shared mailboxes.

#list = children

System user and group used to access mails. If you use multiple, userdb

can override these by returning uid or gid fields. You can use either numbers

or names. <doc/wiki/UserIds.txt>

#mail_uid =
#mail_gid =

Group to enable temporarily for privileged operations. Currently this is

used only with INBOX when either its initial creation or dotlocking fails.

Typically this is set to “mail” to give access to /var/mail.

#mail_privileged_group =

Grant access to these supplementary groups for mail processes. Typically

these are used to set up access to shared mailboxes. Note that it may be

dangerous to set these if users can create symlinks (e.g. if “mail” group is

set here, ln -s /var/mail ~/mail/var could allow a user to delete others’

mailboxes, or ln -s /secret/shared/box ~/mail/mybox would allow reading it).

#mail_access_groups =

Allow full filesystem access to clients. There’s no access checks other than

what the operating system does for the active UID/GID. It works with both

maildir and mboxes, allowing you to prefix mailboxes names with eg. /path/

or ~user/.

#mail_full_filesystem_access = no

Mail processes

Don’t use mmap() at all. This is required if you store indexes to shared

filesystems (NFS or clustered filesystem).

#mmap_disable = no

Rely on O_EXCL to work when creating dotlock files. NFS supports O_EXCL

since version 3, so this should be safe to use nowadays by default.

#dotlock_use_excl = yes

When to use fsync() or fdatasync() calls:

optimized (default): Whenever necessary to avoid losing important data

always: Useful with e.g. NFS when write()s are delayed

never: Never use it (best performance, but crashes can lose data)

#mail_fsync = optimized

Mail storage exists in NFS. Set this to yes to make Dovecot flush NFS caches

whenever needed. If you’re using only a single mail server this isn’t needed.

#mail_nfs_storage = no

Mail index files also exist in NFS. Setting this to yes requires

mmap_disable=yes and fsync_disable=no.

#mail_nfs_index = no

Locking method for index files. Alternatives are fcntl, flock and dotlock.

Dotlocking uses some tricks which may create more disk I/O than other locking

methods. NFS users: flock doesn’t work, remember to change mmap_disable.

#lock_method = fcntl

Directory in which LDA/LMTP temporarily stores incoming mails >128 kB.

#mail_temp_dir = /tmp

Valid UID range for users, defaults to 500 and above. This is mostly

to make sure that users can’t log in as daemons or other system users.

Note that denying root logins is hardcoded to dovecot binary and can’t

be done even if first_valid_uid is set to 0.

#first_valid_uid = 500
#last_valid_uid = 0

Valid GID range for users, defaults to non-root/wheel. Users having

non-valid GID as primary group ID aren’t allowed to log in. If user

belongs to supplementary groups with non-valid GIDs, those groups are

not set.

#first_valid_gid = 1
#last_valid_gid = 0

Maximum allowed length for mail keyword name. It’s only forced when trying

to create new keywords.

#mail_max_keyword_length = 50

‘:’ separated list of directories under which chrooting is allowed for mail

processes (ie. /var/mail will allow chrooting to /var/mail/foo/bar too).

This setting doesn’t affect login_chroot, mail_chroot or auth chroot

settings. If this setting is empty, “/./” in home dirs are ignored.

WARNING: Never add directories here which local users can modify, that

may lead to root exploit. Usually this should be done only if you don’t

allow shell access for users. <doc/wiki/Chrooting.txt>

#valid_chroot_dirs =

Default chroot directory for mail processes. This can be overridden for

specific users in user database by giving /./ in user’s home directory

(eg. /home/./user chroots into /home). Note that usually there is no real

need to do chrooting, Dovecot doesn’t allow users to access files outside

their mail directory anyway. If your home directories are prefixed with

the chroot directory, append “/.” to mail_chroot. <doc/wiki/Chrooting.txt>

#mail_chroot =

UNIX socket path to master authentication server to find users.

This is used by imap (for shared users) and lda.

#auth_socket_path = /var/run/dovecot/auth-userdb

Directory where to look up mail plugins.

#mail_plugin_dir = /usr/lib/dovecot

Space separated list of plugins to load for all services. Plugins specific to

IMAP, LDA, etc. are added to this list in their own .conf files.

#mail_plugins =

Mailbox handling optimizations

The minimum number of mails in a mailbox before updates are done to cache

file. This allows optimizing Dovecot’s behavior to do less disk writes at

the cost of more disk reads.

#mail_cache_min_mail_count = 0

When IDLE command is running, mailbox is checked once in a while to see if

there are any new mails or other changes. This setting defines the minimum

time to wait between those checks. Dovecot can also use dnotify, inotify and

kqueue to find out immediately when changes occur.

#mailbox_idle_check_interval = 30 secs

Save mails with CR+LF instead of plain LF. This makes sending those mails

take less CPU, especially with sendfile() syscall with Linux and FreeBSD.

But it also creates a bit more disk I/O which may just make it slower.

Also note that if other software reads the mboxes/maildirs, they may handle

the extra CRs wrong and cause problems.

#mail_save_crlf = no

Maildir-specific settings

By default LIST command returns all entries in maildir beginning with a dot.

Enabling this option makes Dovecot return only entries which are directories.

This is done by stat()ing each entry, so it causes more disk I/O.

(For systems setting struct dirent->d_type, this check is free and it’s

done always regardless of this setting)

#maildir_stat_dirs = no

When copying a message, do it with hard links whenever possible. This makes

the performance much better, and it’s unlikely to have any side effects.

#maildir_copy_with_hardlinks = yes

Assume Dovecot is the only MUA accessing Maildir: Scan cur/ directory only

when its mtime changes unexpectedly or when we can’t find the mail otherwise.

#maildir_very_dirty_syncs = no

mbox-specific settings

Which locking methods to use for locking mbox. There are four available:

dotlock: Create .lock file. This is the oldest and most NFS-safe

solution. If you want to use /var/mail/ like directory, the users

will need write access to that directory.

dotlock_try: Same as dotlock, but if it fails because of permissions or

because there isn’t enough disk space, just skip it.

fcntl : Use this if possible. Works with NFS too if lockd is used.

flock : May not exist in all systems. Doesn’t work with NFS.

lockf : May not exist in all systems. Doesn’t work with NFS.

You can use multiple locking methods; if you do the order they’re declared

in is important to avoid deadlocks if other MTAs/MUAs are using multiple

locking methods as well. Some operating systems don’t allow using some of

them simultaneously.

#mbox_read_locks = fcntl
#mbox_write_locks = dotlock fcntl
mbox_write_locks = fcntl

Maximum time to wait for lock (all of them) before aborting.

#mbox_lock_timeout = 5 mins

If dotlock exists but the mailbox isn’t modified in any way, override the

lock file after this much time.

#mbox_dotlock_change_timeout = 2 mins

When mbox changes unexpectedly we have to fully read it to find out what

changed. If the mbox is large this can take a long time. Since the change

is usually just a newly appended mail, it’d be faster to simply read the

new mails. If this setting is enabled, Dovecot does this but still safely

fallbacks to re-reading the whole mbox file whenever something in mbox isn’t

how it’s expected to be. The only real downside to this setting is that if

some other MUA changes message flags, Dovecot doesn’t notice it immediately.

Note that a full sync is done with SELECT, EXAMINE, EXPUNGE and CHECK


#mbox_dirty_syncs = yes

Like mbox_dirty_syncs, but don’t do full syncs even with SELECT, EXAMINE,

EXPUNGE or CHECK commands. If this is set, mbox_dirty_syncs is ignored.

#mbox_very_dirty_syncs = no

Delay writing mbox headers until doing a full write sync (EXPUNGE and CHECK

commands and when closing the mailbox). This is especially useful for POP3

where clients often delete all mails. The downside is that our changes

aren’t immediately visible to other MUAs.

#mbox_lazy_writes = yes

If mbox size is smaller than this (e.g. 100k), don’t write index files.

If an index file already exists it’s still read, just not updated.

#mbox_min_index_size = 0

mdbox-specific settings

Maximum dbox file size until it’s rotated.

#mdbox_rotate_size = 2M

Maximum dbox file age until it’s rotated. Typically in days. Day begins

from midnight, so 1d = today, 2d = yesterday, etc. 0 = check disabled.

#mdbox_rotate_interval = 1d

When creating new mdbox files, immediately preallocate their size to

mdbox_rotate_size. This setting currently works only in Linux with some

filesystems (ext4, xfs).

#mdbox_preallocate_space = no

Mail attachments

sdbox and mdbox support saving mail attachments to external files, which

also allows single instance storage for them. Other backends don’t support

this for now.

WARNING: This feature hasn’t been tested much yet. Use at your own risk.

Directory root where to store mail attachments. Disabled, if empty.

#mail_attachment_dir =

Attachments smaller than this aren’t saved externally. It’s also possible to

write a plugin to disable saving specific attachments externally.

#mail_attachment_min_size = 128k

Filesystem backend to use for saving attachments:

posix : No SiS done by Dovecot (but this might help FS’s own deduplication)

sis posix : SiS with immediate byte-by-byte comparison during saving

sis-queue posix : SiS with delayed comparison and deduplication

#mail_attachment_fs = sis posix

Hash format to use in attachment filenames. You can add any text and

variables: %{md4}, %{md5}, %{sha1}, %{sha256}, %{sha512}, %{size}.

Variables can be truncated, e.g. %{sha256:80} returns only first 80 bits

#mail_attachment_hash = %{sha1}

below is /etc/dovecot/conf.d/10-auth.conf

Authentication processes

Disable LOGIN command and all other plaintext authentications unless

SSL/TLS is used (LOGINDISABLED capability). Note that if the remote IP

matches the local IP (ie. you’re connecting from the same computer), the

connection is considered secure and plaintext authentication is allowed.

#disable_plaintext_auth = yes
disable_plaintext_auth = no

Authentication cache size (e.g. 10M). 0 means it’s disabled. Note that

bsdauth, PAM and vpopmail require cache_key to be set for caching to be used.

#auth_cache_size = 0

Time to live for cached data. After TTL expires the cached record is no

longer used, except if the main database lookup returns internal failure.

We also try to handle password changes automatically: If user’s previous

authentication was successful, but this one wasn’t, the cache isn’t used.

For now this works only with plaintext authentication.

#auth_cache_ttl = 1 hour

TTL for negative hits (user not found, password mismatch).

0 disables caching them completely.

#auth_cache_negative_ttl = 1 hour

Space separated list of realms for SASL authentication mechanisms that need

them. You can leave it empty if you don’t want to support multiple realms.

Many clients simply use the first one listed here, so keep the default realm


#auth_realms =

Default realm/domain to use if none was specified. This is used for both

SASL realms and appending @domain to username in plaintext logins.

#auth_default_realm =

List of allowed characters in username. If the user-given username contains

a character not listed in here, the login automatically fails. This is just

an extra check to make sure user can’t exploit any potential quote escaping

vulnerabilities with SQL/LDAP databases. If you want to allow all characters,

set this value to empty.

#auth_username_chars = abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890.-_@

Username character translations before it’s looked up from databases. The

value contains series of from -> to characters. For example “#@/@” means

that ‘#’ and ‘/’ characters are translated to ‘@’.

#auth_username_translation =

Username formatting before it’s looked up from databases. You can use

the standard variables here, eg. %Lu would lowercase the username, %n would

drop away the domain if it was given, or “%n-AT-%d” would change the ‘@’ into

“-AT-”. This translation is done after auth_username_translation changes.

auth_username_format = %Ln

If you want to allow master users to log in by specifying the master

username within the normal username string (ie. not using SASL mechanism’s

support for it), you can specify the separator character here. The format

is then . UW-IMAP uses “*” as the

separator, so that could be a good choice.

#auth_master_user_separator =

Username to use for users logging in with ANONYMOUS SASL mechanism

#auth_anonymous_username = anonymous

Maximum number of dovecot-auth worker processes. They’re used to execute

blocking passdb and userdb queries (eg. MySQL and PAM). They’re

automatically created and destroyed as needed.

#auth_worker_max_count = 30

Host name to use in GSSAPI principal names. The default is to use the

name returned by gethostname(). Use “$ALL” to allow all keytab entries.

#auth_gssapi_hostname =

Kerberos keytab to use for the GSSAPI mechanism. Will use the system

default (usually /etc/krb5.keytab) if not specified.

#auth_krb5_keytab =

Do NTLM and GSS-SPNEGO authentication using Samba’s winbind daemon and

ntlm_auth helper. <doc/wiki/Authentication/Mechanisms/Winbind.txt>

#auth_use_winbind = no

Path for Samba’s ntlm_auth helper binary.

#auth_winbind_helper_path = /usr/bin/ntlm_auth

Time to delay before replying to failed authentications.

#auth_failure_delay = 2 secs

Require a valid SSL client certificate or the authentication fails.

#auth_ssl_require_client_cert = no

Take the username from client’s SSL certificate, using

X509_NAME_get_text_by_NID() which returns the subject’s DN’s


#auth_ssl_username_from_cert = no

Space separated list of wanted authentication mechanisms:

plain login digest-md5 cram-md5 ntlm rpa apop anonymous gssapi otp skey


NOTE: See also disable_plaintext_auth setting.

auth_mechanisms = plain login

Password and user databases

Password database is used to verify user’s password (and nothing more).

You can have multiple passdbs and userdbs. This is useful if you want to

allow both system users (/etc/passwd) and virtual users to login without

duplicating the system users into virtual database.


User database specifies where mails are located and what user/group IDs

own them. For single-UID configuration use “static” userdb.


#!include auth-deny.conf.ext
#!include auth-master.conf.ext

!include auth-system.conf.ext
#!include auth-sql.conf.ext
#!include auth-ldap.conf.ext
#!include auth-passwdfile.conf.ext
#!include auth-checkpassword.conf.ext
#!include auth-vpopmail.conf.ext
#!include auth-static.conf.ext