some mails have correct format date/time, some unixepoch ?

"Voytek Eymont" <voytek@xxxxxxxxxx> · Sat, 27 Oct 2018 15:54:18 +1100

I've just sent a couple of emails, first one has correct Date format, the
second one, has Unix Epoch...
(I think I've had that happen before..??)

what's causing this...?

Received: from 110.xxxxxx
     (SquirrelMail authenticated user voytek@yyy)
     by geko.sbt.net.au with HTTP;
     Sat, 27 Oct 2018 15:41:55 +1100
Message-ID: <0b932436aef000342e55cfb9a0c31504.squirrel@xxxxxxxxxxxxxxx>
Date: 1540615130

Received: from 110.xxxxxx
     (SquirrelMail authenticated user voytek@yyy)
     by geko.sbt.net.au with HTTP;
     Sat, 27 Oct 2018 15:15:27 +1100
Message-ID: <63546d783b3fbd259ec8437c2f90f449.squirrel@xxxxxxxxxxxxxxx>
Date: Sat, 27 Oct 2018 15:15:27 +1100

-- 
Voytek

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