You are getting one of these errors in Znuny, OTRS or OTOBO and you do not know how to fix it?
Sending of this message has failed ... Can't connect to ... !
Email account fetch already fetched by another process. Please try again later!
Try on Znuny Admin page to fix
Analyze and fix on command line
First analyze if you can reproduce the error also on command line with this article How to debug e-mail errors in OTRS / Znuny?