Maxheaderaddrs, maxheaderchars Channel Options

Automatic splitting of long header lines
Some message transports, notably some older sendmail implementations, cannot process long header lines properly. This often leads not just to damaged headers but to erroneous message rejection. Although this is a gross violation of standards it is nevertheless a fairly common problem.

The MTA provides per-channel facilities to split (break) long header lines into multiple, independent header lines. The  channel option  controls how many addresses can appear on a single line. The  channel option controls how many characters can appear on a single line. Both channel options require a single integer argument that specifies the associated limit. By default, no limit is imposed on the length of a header line nor on the number of addresses which may appear.

See also:
 * Headers channel options
 * Channel options