Understanding exim log

Hello,

I have this log below where H = localhost appears and would like to understand why. I tested the webmail and shows the name of the server, by IMAP shows the name of the local machine. I would like to know why localhost appears.

Code:

[root@mx18 /home/someusr/public_html]# exigrep 1gsu1C-003dCu-Hb /var/log/exim_mainlog
2019-02-10 12:39:54 cwd=/var/spool/exim 3 args: /usr/sbin/exim -Mc 1gsu1C-003dCu-Hb

2019-02-10 12:39:54 1gsu1C-003dCu-Hb <= name@example.com H=(localhost) [108.179.xxx.xx]:37164 I=[108.179.xxx.xx]:587 P=esmtpa A=dovecot_plain:name@example.com S=4315 T="Charlotte" from <name@example.com> for name@example.com
2019-02-10 12:39:54 1gsu1C-003dCu-Hb => name <name@example.com> F=<name@example.com> R=virtual_user T=dovecot_virtual_delivery S=4476 C="250 2.0.0 <name@example.com> sM3uJPpvYFx2Mw0AUFo53g Saved"
2019-02-10 12:39:54 1gsu1C-003dCu-Hb Completed

Thank you.

 

Hello,

Thanks rpvw and Lauren for the reply, but my question has not been resolved. My question is because in the log submitted it appears as host "localhost". Because I sent it via webmail and the host name appears. When IMAP sending from an external message manager appears the name of the machine on which the message manager is installed. When sending via SSH, the gateway appears. I am trying to find out by which localhost submission method appears, or if it is random.