Postfix server suddenly is sending with relay= field, any idea?

Posted by StartupTim@reddit | linuxadmin | View on Reddit | 2 comments

I have a postfix server I use for simple development testing. A few days ago, mail started sending like this:

Oct 21 16:26:16 ct2209-debian-12 postfix/smtp[473]: 333AF40890: to=<testtest@emailserver.com>, relay=mx.plingest.com[38.143.66.193]:25, delay=1, delays=0.07/0.01/0.3/0.64, dsn=2.0.0, status=sent (250 2.0.0 Ok: queued as 95ED46780C01)

Notice the relay=mx.plingest.com[38.143.66.193] field?

I have nothing to do with that plingest nor was that configured anywhere. It just suddenly showed up, whereas before there was never a relay= field and mail was sent as normal.

Postfix mail.cf has nothing configured for relaying to an external server.

Any ideas?