sendMails stalling

[Kuchenpferd]

After sending out emails, the script stalls. Left it running for ~30 mins, and keyboard interrupted it afterward. Later the system couldn't send out any emails at all. It was fixed with a complete reboot of the system

EDIT:
It doesn't have to be sendMails. The system also can't send any emails after sending a password email, though the problem isn't evident until you try sending the next mail.