[exim] options to authenticate on my exim server

Hello Everyone,

what are the options (and maybe reading links) to set up secure authenticaiton on my email server?
I'd like to be able to send mails from my android mobile client.
What do you suggest? I already read about examples in /etc/exim4 folders but I don't know if I should use AUTH PLAIN or AUTH LOGIN or else and what layer of encryption as well...
Could you please route me on the good way?

Thanks, best regards