#### 3.19.1 Major differences between Mailutils MH and other MH implementations ¶

1. Sequence numbers increase monotonically;

   Message sequence numbers are used as UIDs and thus increase monotonically. This means, in particular, that if your inbox has messages in the range ‘`X--Y`’ and you delete all messages and then incorporate new mail, the first incorporated message will be assigned sequence number ‘`Y + 1`’ (other MH implementations will assign ‘`1`’). If this behavior bugs you, add the following setting to your `.mh_profile`:

       Volatile-uidnext: true

   You can always renumber your messages starting from ‘`1`’ by running

       folder -pack=1

2. UUCP addresses are not supported;
3. Mailutils supports a set of new format specifications (see New and Differing MH Format Specifications);
4. Mailutils provides a set of new profile variables (see New MH Profile Variables);
5. All programs recognize `--help` and `--version` options

   These options are recognized only if no other arguments are present in the command line. Abbreviations are not recognized. This makes Mailutils MH implementation compatible with the standard usage for GNU tools.

6. Several programs behave differently (see Differences in MH Program Behavior);