Hi,
If the issue only occurs in one mailbox, I don't think it is caused by network ports. Just for your reference, you may refer the following Microsoft article:
http://technet.microsoft.com/en-us/library/bb331973(v=exchg.141).aspx
For the issue you encounter, I'd suggest you change a new mailbox or create a new user account and then try again. Hope it is helpful.
If the issue continues, please check the application event log and the system log for further research. Thanks.
Fiona Liao
TechNet Community Support
