==== REQUIRED BASIC INFO OF YOUR IREDMAIL SERVER ====
- iRedMail version (check /etc/iredmail-release):  1.7.4 MARIADB edition
- Deployed with the downloadable installer       yes
- Linux/BSD distribution name and version:       debian 12.12
- Store mail accounts in which backend           MySQL
- Web server (Apache or Nginx):                     nginx
- Manage mail accounts with iRedAdmin-Pro?    no
- [IMPORTANT] Related original log or error message is required if you're experiencing an issue.
====
I need to test access to SMTP via ssh tunnel. Perhaps IMAP too.

My reason for this is the instability of connection apparently caused by my ISP. SOGo and RoundCube connections are stable, but normal access with mutt (also from Debian 12) fails frequently causing long or permanent feeezes of mutt and frequent failure to save to Sent folder. This behaviour is the same regardless of which remote mailserver I access (Zoho, Migadu, or my iredmail on VPS). It is also repeated on a new minimum install of neomutt.  It seems likely that the frequent dropouts of service ranging from fractions of a second to to several minutes (presumably from excessive contention ratio on the ISP connection) cause the continual reconnects that block the SMTP activity. I observe that ssh connections to the VPS are stable for hours or days, so I believe my email access would be rotected by tunnelling.

So, can anyone point me to simple instructions to access the iRedMail server via ssh tunnel?