Headerlimit Channel Option

Limiting header storage
The MTA stores outermost message headers in memory. This means that a single extremely large header could potentially consume all available memory, possibly leading to a denial of service attack. When placed on a source channel, the  channel option provides a means to prevent such attacks. It accepts a single integer argument specifying the maximum number of MTA blocks that can be consumed by the message header. Messages with headers that exceed this limit will be silently truncated.

Note that the   MTA option can be used to implement the same limit for all channels. The lower of the two option values is used as the actual limit.

The default value for  is essentially unlimited if the channel option isn&#x27;t specified. Note, however, that since the default value for the   MTA option is 2000 blocks, the effective default limit on the size of a header if no limiting options are specified is 2000 blocks.

The  channel option initially appeared in Messaging Server 6.1.

See also:
 * header_limit MTA Option
 * Headers channel options
 * Channel options