Update date of e-mail while processing the queue

Your software
My Mautic version is: v2.15.2
My PHP version is: PHP Version 7.2.19-0ubuntu0.18.04.2

Your problem
My problem is:
We like to warm up our IPs very slowly. We have mautic instance running on our own server. In e-mail settings we selected Queue in “How should e-mail be handled?” and we often manipulate with “Message limit for queue processing” field to reach the expected time-frame while sending e-mails. Of course, we also have proper cronjobs set up.

The problem we are facing is that when we set-up the queue to send e-mails with-in, for example, 2 days - the last e-mails appear in users inboxes with a date of creating e-mail in the queue instead of the date of processing the e-mail queue. So, even when e-mail is delivered in present moment it appears in following way:
[sample read e-mail title]
[sample read e-mail title]
[sample read e-mail title]
[our unread e-mail title]
[sample read e-mail title]
[sample read e-mail title]
[sample read e-mail title]
[sample read e-mail title]

I am not sure where to look for an answer. Is there any option to send e-mails with the date of processing the queue instead of the date of pushing the e-mail into queue? Please note we use localhost postfix to send e-mails and we are warming up dedicated IP. I searched for an answer on GitHub, but I am unsure if this is Bug, Support issue or Feature request so I would be appreciated of pointing me the steps to handle this as soon as possible.

We are developers ourselves, so if you can point us what we need to modify and where to handle this case, we can do that too and we can submit a patch later into your GitHub, though we do not have experience how Mautic is internally built yet.

Also, please note we are sending segment e-mails.