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DeliveriesThe number of message deliveries.# green: to remote recipients. # blue: to local recipients. A delivery is an attempt to deliver a message to its recipient. Every message requires at least one delivery. If that's not successful, more attempts will be made. This is the "upper bound" to the number of messages gone through the server. In normal situations this can be considered a good index of the messages number itself. Queue sizeThe number of messages in the queue.# green: preprocessed. # blue: not preprocessed. The "queue" is a queue of messages waiting to be delivered by the mailserver. When received by the server, every message enters the queue. Its status is "preprocessed" as soon as the mailserver extracts some information about how to handle its delivery, "not preprocessed" until that moment. A large queue is not necessarily synonym of meaningful problems. Today, spam messages bouncing to fake senders can soil heavily the queue. A queue that doesn't stop growing could otherwise point out that the bandwidth available to the mailserver has gotten inadequate. A number of unpreprocessed messages getting bigger and bigger could point out the server has not power enough to handle its traffic. Delivery errorsThe number of unsuccessful deliveries.# green: deferrals. # blue: failures. When a delivery attempt does not succeed an error is encountered. A "deferral" is a temporary error, an attempt which could be successful in the future and that will be retried. A "failure" is a permanent error that won't be retried. Examples of deferrals are storage space full, memory problems, local agent crashes, permission problems on the recipient mailbox or even particular exit statuses of local delivery agents. Examples of permanent errors are deliveries to non-existent recipients, or delivery errors on messages been in the queue too long. Delivery errors is definitely not an index of a mailserver's quality. They can for example point out a temporary situation of heavy traffic for worms. If the number of deferrals grows significantly, the mailserver's bandwidth could have been underrated. Failures growing crazily could mean mess with configurations. ThroughputThe amount of data transferred by the mailserver.# green: bytes transferred. # blue: none. This is the sum of the size of any message gone through the server since the last time checked. A poll interval is commonly 5 minutes or such. The average size of a text-only message is about 2 to 5 KBytes (0.002 to 0.005 MBytes). A message with attachments can reach several MBytes. This is why some graphics could present short peaks and wide flat zones for most of the rest of time. SMTP HitsThe number of smtp connections to the server.# green: the number of hits. # blue: none. An SMTP hit is a connection to the SMTP server. SMTP hits can come from clients or other SMTP servers. A short peak could mean that a some mailserver that had routing problems to us is dumping its queue. SMTP ConcurrencyThe number of concurrent SMTP connections to the server.# green: the maximum concurrency. # blue: the average concurrency. The maximum concurrency is the highest number of concurrent SMTP connections since the last time checked. The average concurrency is the average number of SMTP connections. Maximum and average can differ a lot. Ideally the maximum can reach high values (hundreds), while keeping the average as low as zero. The impact of these cases lowers growing up the average traffic. On busy mailservers (thousand of connections) maximum and average concurrecy should theoretically be very near the one to the other. POP3 HitsThe number of pop connections to the server.# green: the number of hits. # blue: none. Worths much the same story as for "SMTP Hits". POP hits grow commonly faster than SMTP hits growing the number of users: many users like to set an automatic mail check every n minutes. Users with permanent link to the net frequently set their client to check their mail every minute. Paranoid people even a few seconds. POP3 ConcurrencyThe number of concurrent SMTP connections to the server.# green: the maximum concurrency. # blue: the average concurrency. See SMTP concurrency. DNSBL blocked sendersThe number of senders whose connection to the server has been rejected for being listed in some DNSBL.# green: the number of senders (distinguished IPs) rejected. # blue: the total number of connections rejected for DNSBL. The difference between these two values shows the insistence of a source to retry, when you rejected the message permanently. |
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