Hello again.

Today, PMail started spitting messages back at me - see example below

"Delivery has failed on the enclosed message for the following
reasons reported either by the mail delivery system on the mail
relay host or by the local TCP/IP transport module:

550-This is not an open relay. To send through this server you must
either be

Your original mail message follows:

X-PM-Identity: <Default>
From: "Tom Barkas" zen291023@zen.co.uk
To: O&O Software Support support@oo-software.com
Date: Tue, 28 Feb 2023 12:32:23 -0000
MIME-Version: 1.0
Subject: Re: [TicketNr#2023021548001059] Defrag problem
Reply-to: tom@barkas.co.uk"

It doesn't seem to be a Zen Internet problem, as the same messages go as normal if I use Thunderbird. Though the message sounds server-related...
I've installed a VPN today - could this affect messages sent from PMail?

Very likely. IDK why Thunderbird would work though, unless it was not connected to the VPN.

The solution is to change the SMTP port from 25 (blocked because it's used by spammers) to 587 and tick "Log into the SMTP server with the following details"

Probable your ISP allowed port 25 connections from people on there local IP blocks, but when you setup VPN, it would be routing with the VPN's IP, which would not be a local IP, so access requires an authenticated connection versus the original open port 25 connection.