Saw this little blurb in Redmond Magazine and thought I’d pass it on.

If using Exchange 2007’s POP3 service, errors can occure if a UPN ( exceeds 40 characters. 40 characters is the default limit for POP3 as set by the MaxCommandSize setting.

To allow more than 40 character UPN names when using POP3:

1. Open the Exchange Management Shell
2. To review the current POP3 settings, type Get-POPSettings and you’ll see the value for MaxCommandSize among others
3. To increase to 100, type Set-POPSettings -MaxCommandSize 100
4. Restart the POP3 for the changes to take effect.