sendmail, 4th Edition

Whenever an address ^[9] is tokenized, it is stored in a single buffer, one token following the next with a zero-value byte separating them. The size of this buffer is defined by PSBUFSIZ. The default size is defined in sendmail/conf.h as (MAXNAME + MAXATOM).

^[9] For the purpose of tokenizing, rules are also treated as addresses.

In general, this definition should never be changed. If you start getting warning messages such as:

Address too long

look elsewhere (such as rule sets) for the cause. You should consider changing the size of PSBUFSIZ only as a last resort, and then do so with extreme care.