sympa_msg.pl daemon fetches incoming
messages on the incoming spool,
directory. Then it creates an memory image of the message
for later processing. At the end, the processed image is stored into
bulk.pl 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.
- If a message is encrypted and S/MIME certificate of originator is valid, decryption is tried. Later this message may be encrypted again (see below).
Altering message header
X-Sympa-Topicheader field is added as necessity.
See “Message topics”.
If anonymization mode is enabled, several header fields are removed or consealed.
The subject of the message might be changed to add a custom subject tag.
Additional header fields are removed according to customizations.
remove_headersdoes not remove header fields described after this, but
remove_outgoing_headerscan do. Use the latter one only when you know what you are doing, or messages might not be distributed correctly.
Reply-Toheader field is altered according to configuration.
X-Sequenceheader field is added. Its value is the sequence number of posts.
Some header fields are added/removed to prevent mail loop.
See “Loop prevention”.
Senderheader field is added/altered. It should have appropriate value to satisfy some sender domain validation systems such as DKIM, Sender ID.
Header fields configured by
Altering message body
Message body is altered according to message reception mode chosen by each recipient.
See “Message reception modes” for details.
If message personalization is enabled, message body is altered further.
See “Message personalization”.
Encrypting and signing
If DMARC protection is enabled,
Fromheader field is consealed.
See “DMARC protection”.
If original message has been decrypted (i.e. originally encrypted: See above), re-encryption using certificate of recipient is tried. When it fails, a message to inform failure instead of original message is sent to recipient.
See “S/MIME” for further details.
If DKIM support is enabled, DKIM signature invalidated by alterations so far is removed, then message is signed using Sympa’s private key.
If ARC support is enabled, ARC seal is added using Sympa’s private key.
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
The available reception modes can be restricted by listmasters and/or list
owners with the
list/global parameter. list owners can define default reception mode for
users added to the list with
Following changes are made by each mode:
notice: Keeps only the subject of the message. Message body is entirely removed.
txt: Keeps only plain text part of
multipart/alternativemessage. Message content-type is changed from multipart/alternative to text/plain.
urlize: Replaces attachments with the links to the file in message archive. This “urlization” depends on the size of each message part: See also
not_me: Same as
nomail: No delivery.
“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.
“Message header and footer”).
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
htmlreception mode was deprecated on Sympa 6.2.24. Like
txtmode, this mode intended to keep only HTML part of multipart messages, and therefore not practically useful.
If the recipient chooses one of following digest delivery modes, multiple messages are compiled in one message and delivered periodically.
digest: Digest delivery (MIME
digestplain: Digest delivery (plain text format according to RFC 1153).
summary: Digest delivery, sort of: Sends the list of links to message archive.
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.