article applies to Barracuda Email Security Service
The Barracuda Email Security Service (BESS) is an inline or pass-through service.
What that means is that the service handles your mail in real time between your sending mail server and the recipient's destination server.
When you send outbound mail, you connect to the BESS service. BESS accepts your server's connection and the information required to locate the destination server. It then establishes a connection to the destination server and relays your mail in real time. The amount of processing done at each server will determine how long it takes for the mail to arrive at its destination.
- If the sending server investigates each packet for spam and virus content, this will add some latency to the packet heading to BESS.
- BESS will, of course, investigate each packet for spam and virus content. This process will delay the transfer to the destination server slightly more.
- If the destination server investigates each packet for spam and virus content, this process will add a delay the OK going back to BESS.
So to reiterate, each packet of an email message has to go from the SENDER to
BESS to the DESTINATION and then the DESTINATION gives the OK which has
to go from it to BESS and to the SENDER, which can then send the next
packet. Each packet can take up to 5 minutes to process (per the RFC) so
email can potentially take quite a while to be delivered if there are
dozens or hundreds of packets.
In most cases the transfer of packets from the SENDER to BESS to the DESTINATION will only take a few milliseconds, but it is not uncommon to see email servers taking whole seconds to process the data and return the OK for the next packet. These seconds can quickly add up to minutes, especially for mail with attachments, which most mail today has in one fashion or another.
IMPORTANT NOTE: Because BESS acts as a real time relay between the sending and receiving mail servers it is important that connection timeouts on both ends be at least 45 seconds or longer. Having a very short connection timeout can result in delivery failure which delays mail or even prevents mail delivery.