So I have enabled an Ubuntu Server 20 in the cloud with a dedicated public IP, and I want to use it as a SMTP server for MyDomain.com. I have setup DNS and PTR, so this server is mail.MyDomain.com

I have installed Postfix 3.4.13. Then I have created a user with adduser jack

So now, if I login with putty (SSH) to the server as jack, I can succesfully send mails with echo "test" | sendmail Anyone@hotmail.com

The problem is when I am remotely trying to send mail from my laptop (remote network). I can telnet mail.MyDomain.com 25 and send a EHLO command but when I try to use Outlook, I get error

None of the authentication methods supported by this client are supported by your server

Outlook config is:

  • SMTP Server: mail.MyDomain.com
  • user: jack
  • pass: JacksPassw@rd
  • port: 25
  • No Encryption

I've read something about SASL authentication, Dovecot or Cyrus, but I honestly have no idea about this services, nor I'm sure if it's neccesary in a Send Only Email server, as I'm not going to have any incoming mail handled. Our MailBoxes are in a different Server.

What will be the most straightforward way of authenticating as "Jack" from my local Outlook client?? By default, when installing PostFix in Ubuntu, TLS has been enabled, so I wouldn't mind using these as well:

smtp_tls_CApath = /etc/ssl/certs
smtp_tls_security_level = may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache
  • An important consideration. Never use port 25 for email submission from MUAs. It is for inter-server communication, i.e. mail relaying. For client email submission there are ports 576 (with StartTLS might be available), or 465 (where static SSL is configured). See, for example, here: pepipost.com/blog/25-465-587-2525-choose-the-right-smtp-port – Nikita Kipriyanov Feb 19 at 7:08
  • sure.. but first need to get things working. Then I will enable encryption – Jack Casas Feb 19 at 11:31

The error described in the Symptoms section can occur if your Outlook email account is not configured to log on to the incoming server before sending mail, but your Internet Service Provider (ISP) requires you to authenticate before sending email via SMTP.

You can enable the Log on to incoming server before sending mail option for your email account.

How to configure Internet e-mail accounts in Outlook http://support.microsoft.com/kb/287532

  • I understand, but this is not the case. – Jack Casas Feb 19 at 11:30

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