How to calc (md5(md5($pwd).$salt) ?

[philsmd]

This is the algorithm used by the forum software/board VBulletin.

Hence, depending on the salt length, you either need to use -m 2611 (very short salts) or -m 2711 (longer salts).

For examples see https://hashcat.net/wiki/doku.php?id=example_hashes