Hey Manuel, 

Sorry to hear about that. Servers do not accept SMTP connections on ports other than 25, so if you tried to send to Gmail using 587, it wouldn't work. I recommend migrating to another host or looking into using an Outbound Gateway. With an Outbound Gateway, you can send the mail to them over port 587 and they can relay it to the remote servers using port 25. 

I hope this helps. 

Kind Regards, 

Microsoft Azure blocks port 25 on all VMs by default. You may unblock it by creating an Azure Support Request. 

Hi Zach,

Thanks for your quick reply.

If Servers do not accept SMTP connections on ports other than 25, why do Microsoft recomend us to change to Port 587 ??

And CloudFlare ?

     What SMTP port should be used? Port 25 or 587? | Cloudflare

Across the Internet almost every post recommends the use of Port 587 with SSL. If so Its stange that Servers do not accept SMTP connections on ports other than 25 !??

Kind Regards.

Already did thar Ron Raley and the answer was :

I know 3rd party is not the route you want to go - but SMTP2GO will receive your inbounds on one of half-a-dozen ports they have open and run delivery -- prices are very reasonable - support is fast - and they have a viable system for handling SPF and DKIM/DMARC.

They'll work in a pinch till you get sorted on a host. AWS still opens port 25, FWIW.

(not a paid endorsement on either - just that we've used both companies for years without issue) --

I have to agree with Microsoft on this one.   There are two legitimate configurations for cloud hosting:

(1) email hosting systems which enforce good behavior by restricting the system administrator to a "control panel" environment, and

(2) "bare-metal" hosting systems that can do most anything the client wants except use outbound port 25.

When a bare-metal server is not restricted, the spammers buy in.   Then they start spamming with false identities for both the SMTP Mail From address and the message From address.    Once the attack is detected, the evaluator's only defense is to block the hosting service's IP address or server domain name.   Either way, the hosting service gets the black eye.    This attack scenario has happened to me four times in the last year, three times from the same hosting service.   I have suggested strongly, to both hosting services, that they need to implement port 25 restrictions ASAP.

The point of forcing you to use 587 is to force your web server or other non-email application to log onto a mail store server using an authenticated connection, either authenticated SMTP or whitelisted IP address.  Once that is done, the integrity of your message is the responsibility of the mail store server.   If the mail store server is provided by the hosting service, their control panel ensures that you cannot harm their reputation.   If you use a server off their network, the behavior of that server cannot harm the first vendor's reputation.    If you don't want to connect to a mail store server, the alternative is to log onto an email service provider like Sendgrid.net.   This accomplishes the same goal, of preventing impersonation fraud, but you can connect using authenticated API calls instead of authenticated SMTP.

Many Thanks for sharing you experience and point of view Douglas, i'm more convinced now!