WordPress mail problem

Hi, all mail sent from our website to our mail account takes a very long time to get there: about 4 to 24 hrs. This creates a problem with f.i. the timeout of security mailchecks when applying new plugins or working with new software. I contacted our host about this and they can’t solve it. I found out that they are internal IPv6 addresses of the sender’s mail host: mta200a-ord.mtasv.net (104.245.209.200)
And the only thing I can find about this is that the provider of this IP address is called Server Central Network: https://bgp.he.net/ip/104.245.209.200″

Is this something from WordPress?

Thnx in advance

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