javamail - How to send email using third party email server -

i have requirement, registered user can send email thru application using email server how can achieve this?

example: registered user email : user@abc.com,

my email server : mail.xyz.com

now how can user@abc.com can send thru mail.xyz.com both different domains.

please suggest..

if control own email server, can configure allow send mail using email address, although that's bad idea because means people can use email server send spam.

if have protections in place ensure email address you're using legitimate email address registered user, might feel comfortable allowing them send email using mail server.

if application running on server, , can authenticate email server using own username , password, might able configure email server allow send email address want.

if application running on user's server or device, don't want allow have own username , password. in case it's hard provide enough protection ensure email server isn't abused spammers.