Finding Messages to Process
The main saved messages folder and any extra folders specified. Only 20 messages per scan are processed from each 'extra folder' after which scanning continues in the saved messages folder until it empties.
When maintenance mode is enabled, because FS files cannot be written, an interval of 5 minutes occurs between scans; otherwise the interval between scans is 20 seconds.
Loading and Parsing Messages
The message file is loaded, and the first step is to verify the DKIM header if this is specified. DKIM verification involves checking for a .domainkey text record in the DNS records for the sender domain, and verifying that it is valid. Any verification failure is recorded in DKIM_RESULT, but processing continues.
The original message stream is then parsed and the header section of the main part is saved; the header section will be stripped during S/MIME decoding if this is needed.
The parser will warn if the message contains invalid character sequences for the character set in use; this is recorded in the trace, but processing continues.
If present, the Message Information File (MIF) saved by the SMTP server is then loaded. It contains the details of the decryption certificate(s) saved (and encrypted) from the recipient template, as well as the SMTP sender and recipient data, a flag to indicate whether TLS was used, and the substitute sender template returned by a custom gateway DLL, if used.
An error on loading (21) or parsing (22) the message file, or a message file containing no sender (9). prevents further processing of the file.
