SMTP: this message has been in the queue too long
I've installed ISP Config 3 on two servers (multiserver setup) - everything works fine except SMTP.
1) I can send emails from one local account to another local account (using webmail or external mail client)
2) I can send email from ISP to outside servers (using both webmail or external mail client)
but 3) I can't sent from outside servers to ispconfig server - after while I get failure notice: (#4.4.2) I'm not going to try again; this message has been in the queue too long.
Does anybody know what could be wrong? Any ideas?