I forward my work email to my personal GMail account so that I can use
Google Calendar. For some reason meeting invitations are not automatically
added to my Google Calendar unless:

 * They are addressed via the To: line to my GMail address.
 * The ICS attachment reference my GMail address, not my work address.
 * The ICS attachment must be text/calendar, 8bit encoded, named meeting.ics

I've toyed with the secondary email address option on my Google
Account. Doesn't work.

This is a simple utility that parses a MIME email message with an ICS
attachment, substitutes my GMail address, formats the message back into
MIME with the proper attachment settings, and prints it to STDOUT.

I use it as part of my procmail script:

--

:0 HBc
*^TObdixon
* text/calendar
| $TOGMAIL $MVADDR $GMAILADDR | $SENDMAIL -oi -t

:0 a
$STORE_CALENDAR

--

That means:

1) Parse the header and body for emails addressed to bdixon.
2) and with the string "text/calendar" to crudely search for ICS attachments
3) and then filter the message through the script and then pass to sendmail.