Linelength Channel Option

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Restrictions on message line lengths (linelength)

The SMTP specification allows for lines of text containing up to 1000 bytes. However, some transports may impose more severe restrictions on line length, and even some SMTP systems, in violation of the relevant standards, cannot handle full length lines.

The linelength channel option provides a mechanism for limiting the maximum permissible message line length on a channel by channel basis. Messages queued to a given channel with lines longer than the limit specified for that channel will be encoded automatically. The various encodings available always result in a reduction of line length to fewer than 80 characters. The original message may be recovered after such encoding is done by applying an appropriating decoding filter. (In most cases MIME-aware mail user agents are able to detect that such decoding is necessary and perform it automatically.)

Note that encoding can only reduce line lengths to fewer than 80 characters. For this reason specification of line length values less than 80 may not actually produce lines with lengths that comply with the stated restriction.

Note also that linelength causes encoding of data so as to do "soft" line wrapping for transport purposes. The encoding is normally decoded at the receiving side so that the original "long" lines are recovered. For "hard" line wrapping, see instead the "Record,Text" CHARSET-CONVERSION.