Under old versions of sendmail, all lines of text output by sendmail (including the header and body of a message) automatically have the high bit cleared (zeroed) for every character. This behavior remains unchanged under V8 sendmail for configuration file versions 2 or less (Section 17.5). But with version 3 and above configuration files, the message body is transmitted with the high bit intact by default. For those delivery agents that should not allow 8-bit data to be transmitted, you can use the F=7 delivery agent flag to force the old behavior.

Beginning with V8.7, the F=7 delivery agent flag can be used to suppress certain kinds of MIME conversions. For example, if the EightBitMode option (EightBitMode) is set to p (pass 8) and if the message contains 8-bit MIME data in its body, this F=7 delivery agent flag will force sendmail to bounce the message with the following SMTP error, and to exit with EX_DATAERR:

554 5.6.3 Cannot send 8-bit data to 7-bit destination

Note that F=7 affects only the message body. Headers always have the high bit cleared.