Some new emails are not fetched by OTRS

[shawnwangws]

Hey all,
My OTRS is 3.3.5 version running on linux.
I am experiencing the issue that some new emails are skipped of fetching by OTRS although others are working.
The emails without fetching are all sent by one our client's ticketing system with the subject format like '[Category #TicketNumber]Details'.
I tried to forward the messages to another mailbox and they are same to be skipped of getting fetched.
If I removed the [#TicketNumber]from the subject, it could get fetched by OTRS.
However, I couldn't request my client to change their email subject format.
Is there any solution on it?
Thanks.

[jojo]

Check the logs. OTRS does not skip emails without any information. Most likely they use the Same number format like your OTRS, so either you or your customer have to change or you have to rewrite the subject before it reaches OTRS

Please also Note that 3.3.5 is unsecure and outdated so please update.