Try changing «Rule loop Limtt» in SMTP settings .. default it is set to «5»
Open Hmail Server > Settings > Protocol > SMTP > Advanced = Other ->Rule loop Limit ‘5’
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Rule loop count
This option lets you prevent hMailServer from creating endless message delivery loops.
As an example, it’s possible to set up an account rule that forwards message from one user (UserA) to another (UserB), and then another rule that forwards the message back from UserB to UserA.
To prevent this from resulting in an endless loop, hMailServer limits the number of automatic forwards to the value defined by Rule loop count. (hMailServer 4.2 and later.)