With D-Fence the mail size, including attached files, is limited to 30 MB for now. We have discussed this with our technicians earlier, and basically it could be increased but practically not, since it may result in a problem with the connection timeout of SMTP sessions. It is a sender problem.

In practice it means that each time the sending mail server has a certain limited time to finish the transmission. If the mail fails to go through in this time, the process will always start from the beginning. Thereby the problem will be in the connection speed of the sending end.

Now that the D-Fence defence cluster is no longer a normal proxy server unit, but a complete unit dedicated namely for protection, the given time would be exceeded with large mail, and as a result it may still not arrive (even if the large size would be permitted), remaining in the process between the sending server and our server (or would arrive to the recipient even for hundreds of times).

SMTP is not the proper protocol for sending large files, and for the above-named reasons a special protocol is developed, which is in extensive use by advertising, media and designing offices. This is the FTP.

One alternative would be to send the mail in pieces, so that it would come through also in SMTP. Some operators have limited the largest mail size to 20 MB, meaning that it would be risky to send an e-mail of even a few MB as an SMTP file.