I am getting the below messsage in /var/adm/message after patching but sendmail is working after restoring the backup file.
sendmail[14775]: [ID 801593 mail.crit] q4G7U1Cj014774: SYSERR(root): 127.0.0.1 config error: mail loops back to me (MX problem?)
sendmail[25828]: [ID 801593 mail.crit] q4G801cw025824: SYSERR(root): 127.0.0.1 config error: mail loops back to me (MX problem?)
sendmail[5196]: [ID 801593 mail.crit] q4G8U1YQ005195: SYSERR(root): 127.0.0.1 config error: mail loops back to me (MX problem?)
Sounds like either your sendmail config was borked by the patch or you have zonefiles misconfigured for your domain (if you aren't running your own DNS, this is less likely). I seem to recall having this happen while configuring sendmail in the late 90s. This page has a decent overview -