I sent out a invites. a few minutes later I got error email from 5 of the addresses

as non deliverable. then the same returns kept coming every few minutes. at first I thought that it was automatic re deliverys from my SMTP account. But they kept coming again and again until I disabled my cron jonb then they stopped . I waited 30 minutes and reenabled the cron and they started again, its like the site is in a endless loop.

using 1and 1 hosting service

SMTP  for email from site

Oxwall 1.5.x latest updates

disabling smtp on site did not stop this but disabling the cron job did

any ideas what is happening

the emails to the bad addresses retried more than 50 times before I got it stopped and I am afraid that the valid addresses also got 50 emails also