Linelength Channel Option

Soft wrap (encode) long lines in messages
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.

First the MTA performs any appropriate header line wrapping: see the  channel option. Then the  channel option provides a mechanism for limiting the maximum permissible message body line length on a channel by channel basis. Messages queued to a given channel with body lines longer than the  limit specified for that channel will have the message body  encoded automatically. (Note that  is a destination channel option modifying what the MTA emits; for controlling how the MTA handles illegally long lines that it receives via SMTP, see instead the    options.) 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  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".

The default for arbitrary channels is 1023 channels; but channels marked with an  or   channel option will not allow more than 998 characters and attempts to set   larger (or not setting   explicitly on such channels) will result in using 998 characters on such channels.

See also:
 * CHARSET-CONVERSION mapping table
 * smtp Option
 * lmtp Option
 * headerlinelength Option
 * rejectsmtplonglines Option
 * Attachments and MIME processing channel options
 * Channel options