+The `checkalias' option (normally off) extends the lookups performed
+by the `dns' keyword in multidrop mode, providing a way to cope with
+remote MTAs that identify themselves using their canonical name, while
+they're polled using an alias.
+When such a server is polled, checks to extract the envelope address
+fail, and
+.IR fetchmail
+reverts to delivery using the To/Cc/Bcc headers (See below
+`Header vs. Envelope addresses').
+Specifying this option instructs
+.IR fetchmail
+to retrieve all the IP addresses associated with both the poll name
+and the name used by the remote MTA and to do a comparison of the IP
+addresses. This comes in handy in situations where the remote server
+undergoes frequent canonical name changes, that would otherwise
+require modifications to the rcfile. `checkalias' has no effect if
+`no dns' is specified in the rcfile.
+.PP