i have recived this error when send mail using aapanel webmail plugin. i am face this issue after upgrade mail server plugin.
Failed to send mail, error reason [SMTP AUTH extension not supported by server.]
hear is mail server log file.
Mar 6 14:13:36 cluster postfix/smtpd[30723]: connect from localhost[::1]
Mar 6 14:13:36 cluster postfix/smtpd[30723]: lost connection after EHLO from localhost[::1]
Mar 6 14:13:36 cluster postfix/smtpd[30723]: disconnect from localhost[::1] ehlo=1 commands=1
Mar 6 14:14:05 cluster dovecot: imap-login: Login: user=<crimsion@securevault.xyz>, method=PLAIN, rip=155.138.141.114, lip=155.138.141.114, mpid=30793, TLS, session=<SRiFjymg6oybio1y>
Mar 6 14:14:05 cluster dovecot: imap(crimsion@securevault.xyz): Warning: autocreate plugin is deprecated, use mailbox { auto } setting instead
Mar 6 14:14:05 cluster dovecot: imap(crimsion@securevault.xyz): Logged out in=89 out=955
Mar 6 14:14:24 cluster dovecot: pop3-login: Aborted login (auth failed, 1 attempts in 2 secs): user=<info@angelbizlink.co.in>, method=PLAIN, rip=89.248.174.39, lip=155.138.141.114, session=<OVuBkCmg9ktZ+K4n>