Can't send mail via mail clients

basically i can’t send email as i get a password auth error with a known correct password using let encrypt and ssl

CentOS Linux 7.6.1810

The server software
Postfix version 2.10.1
Dovecot IMAP/POP3 Server
Version 2.2.36
MySQL Database Server
MySQL version 10.4.8-MariaDB

This is on a testing server, as i can mess with it. On my production server, its doing the same thing but i’m having issues loging in and also some aren’t excepting @ and - even with the -r flag for postfix.

The postfix version is 2.10.1 which is classed eol.

Will upgrading to postfix to 3.x will solve the ssl auth issue. ?

I can send mail via usermin on both servers