One way to reduce if not totally eliminate spam created by spambots is by implementing traffic filters to block outbound request to TCP port 25, which will prevent bare metal and dedicated virtual server instances from sending direct outbound email using port 25. It is critical that you investigate your software, scripts and web applications to determine if they are sending direct outbound email. Once these changes are implemented, your public IP addresses will cease to have access to send email traffic outbound via TCP port 25, and any direct email which is made by your systems will need to route through an SMTP relay (typically TCP port 587 or 465) or through alternate port, 26 in the local server. SMTP APIs that are configured to send via port 25 will also cease to function.
Since last year, our knowledgebase entries and our support team encourages the use of port 26 or port 587 to configure e-mail softwares like MS Outlook. For shared hosting accounts, if you are already using ports 26 or 587 instead of port 25, you do not have to do anything.
If you are using your baremetal server, dedicated VPS or your shared hosting account for website hosting purposes only and not for e-mail and your website is not sending out any mail notification via port 25, then you are not affected by this change. If you have an unmanaged dedicated server, you will have to use an SMTP relay to send out e-mail messages.
To customers who are sending bulk mail, IBM has partnered with SendGrid and is providing each customer with an account at no cost which allows sending of up to 25,000 emails/month. We are now using http://www.mailchannels.com/ and we also recommend as an alternative option.
You may also utilize one of the many SMTP relay services available (https://www.google.com/search?hl=en&q=smtp+service+providers) on the Internet.
How to change SMTP port in Outlook?
Kindly check this link for more information.
Monday, January 11, 2016