Trying to fix 550-From header sender domain not verified

[arminus]

I have the following setup: Postfix running on the server for the MX record of mydomain.com, configured with a relayhost which requires sender domains/addresses to be verified. So basically, I can send messages from that server out, but if I try to forward some incoming mail via the relayhost to an external email address, it blocks with a 550.

So someone suggest I'd use postrsd to rewrite the sender address in this case, but unfortunately, this doesn't sem to work or I miss something in the config.

Here's what I set in postsrsd.conf so far:

domains = { "mydomain.com" }
srs-domain = { "mydomain.com" }

everything else is default, the respective postfix main.cf is copied form the install steps here.

Now when an email comes in which is supposed to be rerouted via a postfix virtualmap entry reroute@external.com test@mydomain.com, I get this:

Oct 21 10:30:02 myserver postfix/smtp[377165]: E7F8D180179: to=<reroute@external.com>, orig_to=<test@mydomain.com>, relay=mail.smtp2go.com[139.162.187.151]:587, delay=1.3, delays=0.06/0.02/0.57/0.62, dsn=5.0.0, status=bounced (host <external relayhost> said: 550-From header sender domain not verified (external-sender-domain.com) 550-On your Sending > Verified Senders page 550 verify the sender domain or email to be allowed to send. (in reply to end of DATA command))
Oct 21 10:30:02 myserver postsrsd[377164]: postsrsd: <SRS0=MUYl=GD=external-sender-domain.com=external-sender@mydomain.com> reversed to <external-sender@external-sender-domain.com>
Oct 21 10:30:02 myserver postsrsd[377164]: postsrsd: <SRS0=MUYl=GD=external-sender-domain.com=external-sender@mydomain.com> reversed to <external-sender@external-sender-domain.com>

There are 2 things which I can conclude from this:

• the relay server is apparently contacted before postsrsd attempts to do its rewrite
• the rewrite apparently doesn't work

What I would kind of expect is that the rewrite would change the sender from external-sender@external-sender-domain.com to external-sender@mydomain.com, but that doesn't seem to happen. And maybe the order of the log entries is misleading and the inly issue is the nit working rewrite.

Or isn't postsrsd suitable for that scenario to begin with?