I’ve noticed if I put in the Virtualmin suggested configuration for an e-mail client into an iPhone, it seems to get stuck in the “Verifying” stage.
If I look at the e-mail configuration page for any given user in Virtualmin, it says “Use SSL for SMTP? No,” which made me wonder if that might be associated with the problem.
Perhaps relatedly: I also enabled “e-mail client auto configuration” under E-mail Settings → Mail Client Configuration in Virtualmin, but that doesn’t seem to help with configuration either iOS or macOS’s mail client. Do I need to do something else on that end? The auto configuration URL seems to be loading just fine if I try to load it manually, so I don’t think that is the issue.
Virtualmin sets up SMTPS and Submission with STARTTLS. STARTTLS is probably preferable to SMTPS, though both are encrypted.
And, of course, POP and IMAP are available in their TLS encrypted versions.
You probably want to look at the mail log or the journal for the relevant service unit when you’re trying to connect (maybe postfix or saslauthd) to see what kind of mess is happening.
That message I mentioned is showing up on the “Show E-mail Client Settings” page in Virtualmin itself.
Like I said, not sure if it is connected, but auto discovery definitely isn’t working (not sure if it supports Apple’s auto discovery techniques?) and it does seem to freeze up when trying to verify account settings on iOS. This could be an entirely different issue or perhaps the message in Virtualmin is a canary in my e-mail coal mine… I’ll try to see if I can find anything more in the logs.