Tomas provided patch which was positively tested.
Re-proposed to 4.7
This request was evaluated by Red Hat Product Management for inclusion, but this component is not scheduled to be updated in the current Red Hat Enterprise Linux release. If you would like this request to be reviewed for the next minor release, ask your support representative to set the next rhel-x.y flag to "?".
Found some issues in that patch. encodeHeaderBase64 function was not written to handle 7bit charsets with escape sequences. It will work correctly only with short unfolded headers.
Sorry. false alarm. Function does not know about iso-2022 escapes, but mbstring extension knows them and splits string correctly.
I'm sorry for not addressing the issue in RHEL-4. As squirrelmail is not scheduled for update in RHEL-4.9, I'm closing that bugzilla WONTFIX. If you are still experiencing the issue with RHEL-5, feel free to reopen it against RHEL-5.