Why do different email accounts on my server have different file structures?

Question

Why do different email accounts on my server have different file structure?

Answer

The server can use two different types of storage systems for email on the server - mdbox and maildir.  If you have migrated one account from another it's possible it was using a different storage format, and the files will look different on the server.  Here is an example of the file structure in /home/username/mail/domain.com/email with both MDBox and Maildir:

MDBox:

/home/usename/mail/domain.com/email]cPs# ll
total 116
-rw-r----- 1 username username 0 Feb 5 2018 dovecot-acl-list
-rw-r----- 1 username username 1136 Feb 1 2019 dovecot.index
-rw-r----- 1 username username 64980 Feb 6 2019 dovecot.index.cache
-rw-r----- 1 username username 4372 Feb 6 2019 dovecot.index.log
-rw-r----- 1 username username 1024 Aug 27 23:04 dovecot.list.index
-rw-r----- 1 username username 1944 Aug 28 11:03 dovecot.list.index.log
-rw-r----- 1 username username 72 Apr 4 2019 dovecot.mailbox.log
-rw-r----- 1 username username 53 Aug 28 11:03 dovecot-quota
-rw-r----- 1 username username 7614 Feb 6 2019 dovecot-uidlist
-rw-r----- 1 username username 8 Apr 4 2019 dovecot-uidvalidity
-rw-r----- 1 username username 0 Nov 27 2017 dovecot-uidvalidity.5a1c0c01
drwxr-x--x 9 username username 97 Apr 4 2019 mailboxes
-rw-r----- 1 username username 5 Feb 6 2019 mailbox_format.cpanel
-rw------- 1 username username 2049 Feb 6 2019 maildirsize
drwxr-x--x 2 username username 177 Aug 28 07:29 storage
-rw-r----- 1 username username 18 Apr 4 2019 subscriptions

Maildir:

/home/username/mail/domain.com/email]# ll
total 72
drwxr-x--x 11 username username 4096 Jul 17 10:17 ./
drwxr-x--x 3 username username 4096 May 9 2018 ../
drwxr-x--x 5 username username 4096 Jul 17 10:17 .Archive/
drwxr-x--x 2 username username 4096 May 9 2018 cur/
-rw-r----- 1 username username 0 Jul 17 10:17 dovecot-acl-list
-rw-r----- 1 username username 160 Jul 17 10:17 dovecot.index.log
-rw-r----- 1 username username 2396 Jul 17 10:17 dovecot.list.index.log
-rw-r----- 1 username username 48 Jul 17 10:17 dovecot.mailbox.log
-rw-r----- 1 username username 51 Jul 17 10:17 dovecot-uidlist
-rw-r----- 1 username username 8 Jul 17 10:17 dovecot-uidvalidity
-r--r--r-- 1 username username 0 May 13 2019 dovecot-uidvalidity.5cd9cd10
drwxr-x--x 5 username username 4096 Jul 17 10:17 .Drafts/
drwxr-x--x 5 username username 4096 May 13 2019 .Junk/
-rw------- 1 username username 18 May 9 2018 maildirsize
drwxr-x--x 2 username username 4096 May 9 2018 new/
drwxr-x--x 5 username username 4096 Jul 17 10:17 .Sent/
drwxr-x--x 5 username username 4096 Jul 17 10:17 .spam/
-rw-r----- 1 username username 18 Jul 17 10:17 subscriptions
drwxr-x--x 2 username username 4096 Jul 17 10:17 tmp/
drwxr-x--x 5 username username 4096 Jul 17 10:17 .Trash/

If you'd like to convert an account to use a different mailbox storage system we have the Mailbox Conversion tool in WHM that handles this automatically for you.