How can I change hostname in exim mainlog?

I used roundcube webmail.
How can I change H=(otherdomain.com) [127.0.0.1] to H=(mydomain.com) [127.0.0.1], please see the log.

The following information is my mainlog file:
2017-06-29 17:59:03 1dQXA7-0000hg-Pg <= myname@mydomaincom H=(otherdomain.com) [127.0.0.1] P=esmtpa A=login:myname@mydomaincom S=788 id=1a87f75100b9463602d8affb2f5c0f7a@mydomain.com T="Subject" from <myname@mydomaincom> for mycustomer@hotmail.com
2017-06-29 17:59:03 cwd=/var/spool/exim 3 args: /usr/sbin/exim -Mc 1dQXA7-0000hg-Pg
2017-06-29 17:59:12 1dQXA7-0000hg-Pg => mycustomer@hotmail.com F=<myname@mydomaincom> R=lookuphost T=remote_smtp S=1694 H=mx2.hotmail.com [104.44.194.234] X=TLSv1.2:ECDHE-RSA-AES256-SHA384:256 CV=yes C="250 <1a87f75100b9463602d8affb2f5c0f7a@mydomain.com> Queued mail for delivery"
2017-06-29 17:59:12 1dQXA7-0000hg-Pg Completed

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