CleanMail - Email Archiving
A mail storage can be inserted into the filter pipeline at an arbitrary position. Depending on the position, mails can be saved as they have been received (mail storage is the first filter), or after filtering (mail storage is the last filter). Mails are stored as files in standard MIME-Format (RFC-822) in a directory of your choice on your server.
The mail files can be viewed with the majority of mail client software. In addition to the mail file, message transmission data, such as the SMTP sender and recipients, are stored in a separate 'envelope' file. The envelope file can be viewed with a text editor.
Stored messages can also be used in CleanMail's learning functions, for example to train the SpamAssassin Bayes database.
If the mail storage is the first filter, it will also cache messages that have been classified as spam and deleted (if your spam policy is to delete messages). If a message is misclassified and lost (false positive), you can use this to forward the message from the mail storage to the intended recipient.