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CentOS | Sendmail

On occasion I've noticed that completely separate messages going through a common SendMail server may have very similar SendMail QIDs.

For example one message may have a QID of r5SGTeQb019223 and another may have r5SGTEQb019223 (the difference being the case sensitivity of the E).

Why is this? Is it just coincidence or are there specific rules that determine how these QIDs are generated and what they should be?

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up vote 1 down vote accepted

From page 397 of the bat book:

For V8.10 sendmail, the identifier is constructed differently. Each character stands for (in this order, reading left to right): the year (minus 1900) modulo 60, the month, the day, the hour, the minute, the second, and a sequence within the second that starts at a random value

The whole chapter goes in great detail on the different queue naming schemes that are used by different versions of sendmail

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