What do you mean by "email server"?
Do you want to actually host your own email domain server on your phone?
To what end and purpose?
Most have stopped hosting their own email servers - which was typically on some version of Unix, Linux or Windows Server boxes. Businesses generally quit doing it years ago, switching to MS-365 exchange services instead while keeping their "corporate-dot-com" addresses.
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Sure, there are a few brave souls out there still truckin' along. But is a cellphone really going handle an email server?
It's going to be more than just some apk you install anyway. I'm pretty sure you would have to set the device up as a server too in some way. Talk about killing the battery too.
If I'm wrong about it, good luck.