[FEAT] Add Fetchmail + relayhost AUTH support

[armandofcom]

Agregar soporte para recoger los correos de un domainpop y el envío de correo autentificado en un servidor externo

/

Add domianpop (multipop, multidrop) fetching from a master server.

[stdevPavelmc]

If we talk about fetchmail, then we must include relayhost AUTH support, that's a security feature we can't miss.

[stdevPavelmc]

Anyone using fetchmail to test this?

Code is on #167

I have no means of test this now.