Array
(
    [aspmx.l.google.com] => 1
    [alt1.aspmx.l.google.com] => 5
    [alt2.aspmx.l.google.com] => 5
    [aspmx2.googlemail.com] => 10
    [aspmx3.googlemail.com] => 10
    [aspmx4.googlemail.com] => 10
    [aspmx5.googlemail.com] => 10
    [colef.mx] => 0
)

try aspmx.l.google.com:25

<<<
220 mx.google.com ESMTP j19-20020a17090aeb1300b002a2c731f51dsi9309792pjz.133 - gsmtp

>>>
HELO colef.mx

<<<
250 mx.google.com at your service

>>>
MAIL FROM: <edelman@colef.mx>

<<<
250 2.1.0 OK j19-20020a17090aeb1300b002a2c731f51dsi9309792pjz.133 - gsmtp

>>>
RCPT TO: <valentin@colef.mx>

<<<
250 2.1.5 OK j19-20020a17090aeb1300b002a2c731f51dsi9309792pjz.133 - gsmtp

>>>
RSET

<<<
250 2.1.5 Flushed j19-20020a17090aeb1300b002a2c731f51dsi9309792pjz.133 - gsmtp

>>>
quit

<<<
221 2.0.0 closing connection j19-20020a17090aeb1300b002a2c731f51dsi9309792pjz.133 - gsmtp