Mailgun SMTP times out

Install/Maintain/Configure
1

Followed the instructions here: How to set up email registration

[mailer]
ENABLED = true
HOST    = smtp.mailgun.org:587
FROM    = no-reply@domain.tld
USER    = postmaster@domain.tld
PASSWD  = mailgun-password
USE_SENDMAIL=false

It just times out, how can I debug this? I also have UFW enabled.