Symptoms
Unable to view some emails in webmail and /var/log/maillog shows
failed: Invalid quoted-printable input trailer: '=' not followed by two hex digits
Workaround
The following will allow those emails to be visible in webmail.
cp -ax /var/cpanel/templates/dovecot/main.default /var/cpanel/templates/dovecot/main.local
Then modify /var/cpanel/templates/dovecot2.3/main.local and edit this section
[%- IF protocol_imap.imap_capability.defined %]
imap_capability = [% protocol_imap.imap_capability %]
[%- ELSE %]
#imap_capability =
[%- END %]
to instead be
[%- IF protocol_imap.imap_capability.defined %]
imap_capability = "IMAP4rev1 SASL-IR LOGIN-REFERRALS ID ENABLE IDLE SORT SORT=DISPLAY THREAD=REFERENCES THREAD=REFS THREAD=ORDEREDSUBJECT MULTIAPPEND URL-PARTIAL CATENATE UNSELECT CHILDREN NAMESPACE UIDPLUS LIST-EXTENDED I18NLEVEL=1 CONDSTORE QRESYNC ESEARCH ESORT SEARCHRES WITHIN CONTEXT=SEARCH LIST-STATUS MOVE"
# imap_capability = [% protocol_imap.imap_capability %]
[%- ELSE %]
#imap_capability =
[%- END %]
and then run the following
/scripts/builddovecotconf
/scripts/restartsrv_dovecot