The size of an incoming SMTP message is the number of bytes sent during the DATA phase (See this section), including end-of-line characters. The size of a message received via sendmail's standard input is a count of the bytes received, including the newline characters. In both instances the size is displayed with the size= syslog equate:

size=23

Note that this size is reported before sendmail adds or deletes any headers. Therefore, for mail being relayed through a site, the size will usually be small coming in and somewhat larger going out.

The size= syslog equate is produced only for sender records.