Two mail servers

[lukastribus]

No, this is not possible, for the reasons mentioned here:

IMAP + SMTP proxy for 2 Mail Domains

You can’t. Haproxy does not know about SMTP or IMAP, and therefor cannot make load-balancing decision based on that. Also, the destination email address is unknown when the connection establishes first (and when the first packet is send) - which is when a load-balancing decision has to take place (unless the proxy itself is a full-blown SMTP/IMAP speaker). So this really requires a software that is actually able to dialog in SMTP/IMAP with the client, which haproxy isn’t.