We have just the same problem of a broken image link at the very end of the email when using MailPress 5.1.1.
The faulty image URL is practically the same as the URL for “Manage your subscriptions” which is generated from the footer.php file of MailPress.
Broken Image URL: … action.php?tg=o&mm …
Working Subscription URL: … action.php?tg=l&mm …
While there is no functionality problem, the broken image link leaves a poor impression when sending out newsletters.
Any idea?