Simple DNAT but blunted?

Question

Mikrotik

Good afternoon,
like a common question but blunted.
The client cannot connect to the mail server 25 (TCP) directly (the server is blocked), he decided to transfer requests to me and throw his Mikrotik to the mail server, nat rule:
chain=dstnat action=dst-nat to-addresses=mail server to-ports =25 protocol=tcp dst-address=my mikrotik in-interface=WAN1 dst-port=9090 log=no log-prefix=""
In fact, it turns out that the client accesses my server on port 9090, then the microtik should transfer it to the mailer and already on port 25. (It seems to me that the package does not know how to get to the client (in the right form)?)
In fact, it seems to be true, but I missed something, there are no more rules in NAT, I turned off the firewall (prohibitions) for the duration of the tests.
Added #1:
Mikrotik and mailer - have white addresses.

Answer 1

Taxi, is your mailman located on the local network or somewhere?