Culprit : 

#define EXTRACT_FIRST_STRING(val) len=strtoul (part, &part, 10); part++; val=g_strndup (part, len);
#define EXTRACT_STRING(val) part++; len=strtoul (part, &part, 10); part++; val=g_strndup (part, len);
#define EXTRACT_FIRST_DIGIT(val) val=strtoul (part, &part, 10);
#define EXTRACT_DIGIT(val) part++; val=strtoul (part, &part, 10);

and itz usage in message_info_from_db (CamelFolderSummary *s, CamelMIRecord *record).

Looks like the expected count from cinfo is not being put in the expected position in the DB. So in my db : 
sqlite> select cinfo from Inbox

 9-multipart 11-alternative 1 8-boundary 28-____UZJSHDHNGATVUEGXPUDO____ 0- 0- 0- 0 0

I think the 'count' is expected at position 1 but somehow moved to position 3 which screwsup the entire parsing leading to overflow .. 

Also add more checks for strtoul (errno, ret val == ULONG_MAX .. )

Could migration code be responsible for this ? 

Johnny, No. This is some serious issue. Lemme see. I have never tested played with cinfo. IMAP provider right?

Yep. IMAP.

Bug fixed in this revision.
http://svn.gnome.org/viewvc/evolution-data-server?view=revision&revision=9192

Closing.