Demo
Demo

Knowledge base

PMTA knowledge base›Mechanism§ 4.2.4

The line ending requirement

line termination in submitted mail
The most common submission error

The manual calls ending lines with a single LF instead of the CRLF pair required by mail standards the most common error of a program that submits messages to the node.

It is diagnosed with a session recording: a <source> block for the submitting program’s address with log-connections and log-commands shows at which transfer step — for example, at the RCPT command — the failure happens, and log-data prints every byte with its hexadecimal code, so the missing CR becomes visible.

The submission bindings are more forgiving here: with 7-bit and 8-bit encodings they convert a lone LF to CRLF themselves.

The main trap is testing the program only through a binding. The binding fixes a lone LF itself, and the error is invisible; the same program submitting over SMTP will start failing.
What the Hub does. The Hub itself submits warm-up messages to the node over SMTP, so this requirement applies to it too; on someone else’s platform it is the first thing to check when submission fails strangely.
Recommended values

What to turn on for diagnosis:

Directive What it writes
log-connections connections
log-commands commands and replies
log-data data with hexadecimal byte codes
The most common error and diagnosis with a session recording come from the manual (§ 4.2.4); LF conversion in the bindings is § 7.4.10. The trap analysis is ours.
Example configuration
<source 127.0.0.1>
    log-connections yes
    log-commands yes
    log-data yes</source>
An example from the manual; after the edit the configuration is reloaded, and the block is removed as soon as the cause is found.
yellow — — directive names, blue — blocks. They are highlighted the same way in the text of the card.
Compatibility
PowerMTA 6.0
described in the manual of this version · platform: any
The vendor does not state the first version for every directive — there is no note here. The name also appears in the 5.0 edition of the manual.
⇄

Related entries

2 relations

Applies to

How a message gets into the engineA related mechanism: they work together. inference

Where you can see it

Troubleshooting mail receptionThe procedure in which the mechanism is applied. § 4.2.4

Referenced from

Encodings at submissionA related mechanism: they work together. § 7.4.10

How to check on the node
With recording on, look at the session in the log:
pmta reload
tail -100 /var/log/pmta/log
In the data recording, CR and LF show as the codes 0d and 0a: a lone 0a without 0d before it is an error of the submitting program. The log path comes from log-file.
◇

What else to read

3 articles

◇How a message gets into the engineSix described submission methods: extended SMTP, four language bindings and a directory the node watches on disk.◇Who is allowed to submit mail and for whom to accept itOut of the box, the node accepts submission only from the machine itself; two different questions — “who can send through us” and “for whose addresses we accept mail” — are answered by different directives.◇Headers the sender uses to control deliverySix control headers let the submitting side choose a stream, tag a message with a job, set signing options and the key, the envelope identifier and the schedule; each is allowed separately and per source.

In the Hub
Cost of a mistake
safe: a wrong value breaks nothing
Scenarios
Connect a sending platform