HAProxy for imap - Backend behind WireGuard

[Bronko]

Hi,

pfsense 2.7.2-RELEASE (amd64) on VPS (A) with HAProxy, Backend target is on private network behind second pfsense box (B), both connected by wireguard package.

Dovecot on private server (Backend target) is awaiting imap connections prepared for haproxy on port 10143. Packets are flowing in both directions (packet sniffer and wireshark confirmed) but no imap connection established.

haproxy log:

Dec 10 00:03:05 mail haproxy[47893]: IP_MASKED_for_PRIVACY:58902 [10/Dec/2023:00:02:59.959] imap iredmail-imap_ipv4/imap-send-proxy-v2 1/25/5066 0 -- 1/1/0/0/0 0/0

dovecot log:

mx dovecot: imap-login: Error: haproxy: Client timed out (rip=WG_Interface_A)

or sometimes:

mx dovecot: imap-login: Error: haproxy: Client disconnected: Failed to read valid HAproxy data (rip=WG_Interface_A)

Did not find any for an advanced monitoring (haproxy logging is on Debugging).

Any hints for me?