When sendmail is required to convert a message body into quoted-printable form as determined by the EightBitMode option (EightBitMode), it ordinarily converts only those characters that are required by RFC1521. Unfortunately, mail that is transmitted to some IBM machines (specifically those that speak EBCDIC instead of ASCII) can become garbled because of the way EBCDIC represents (or fails to represent) certain characters. Those characters are:

! " # $ @ \ [  ] ^ ` { | } ~

When sending MIME mail to such sites, you should probably set the F=3 delivery agent flag for any delivery agents that handle those sites. Setting this delivery agent flag tells sendmail to encode those characters, in addition to those normally encoded, using quoted-printable.

Note that sendmail does this encoding only if 8-bit characters appear in the message. This delivery agent flag solves one EBCDIC problem but should not be thought of as a general solution for all EBCDIC problems.