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Message alteration

Sympa's daemon fetches incoming messages on the incoming spool, $SPOOLDIR/msg directory. Then it creates an memory image of the message for later processing. At the end, the processed image is stored into outgoing spool, $SPOOLDIR/bulk directory, and daemon fetches and dumps it to the mail transfer agent (MTA).

Does Sympa alter messages?

The intermediate image described above might be altered. However, if a message is S/MIME signed, it should not be altered, because any changes in any part of the message body would break integrity of the S/MIME signature.

Sympa might perform the following changes to the messages to be distributed. Some of these alterations can be configured.


Altering message header

Altering message body

Encrypting and signing

Eventually, the message is delivered to recipient by the MTA.

Message reception modes

List members can choose the reception mode of their own either through the web interface or via the SET list mode mail command.

The available reception modes can be restricted by listmasters and/or list owners with the available_user_options list/global parameter. list owners can define default reception mode for users added to the list with default_user_options list parameter.

Following changes are made by each mode:

Regular delivery

Additionally with mail, not_me, txt or urlize mode, "header" and/or "footer" may be added. They are either added as separate MIME parts, or within the message body if it is of text type. See "Message header and footer").

However, mail and not_me modes do not alter S/MIME signed message (i.e. its MIME type is multipart/signed) so that integrity of signature will not be broken.


  • html reception mode was deprecated on Sympa 6.2.24. Like txt mode, this mode intended to keep only HTML part of multipart messages, and therefore not practically useful.

Digest delivery

If the recipient chooses one of following digest delivery modes, multiple messages are compiled in one message and delivered periodically.

With digest mode, the body of each message compiled in is not altered. the other modes does not keep signature.

However, encrypted messages are never included in compiled message.

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