Struggling to find out the right SMTP port to use? Been there, done that!
If you’re using an email client like Apple Mail or Outlook to send emails, that email client probably also uses SMTP to upload your outgoing emails to your mail server (though those clients typically use other protocols like IMAP or POP3 to download incoming emails to the app).
Additionally, if you’re struggling with email deliverability on WordPress, one of the best ways to fix the problem is to use an SMTP sending service like SendGrid, Mailgun, or G Suite.
But if you try to set up SMTP with your email client or WordPress website, you’ll probably encounter the question of which SMTP port to use.
To help you choose the right SMTP port for your needs, we’re going to dig into everything SMTP port-related in this post.
What is an SMTP Port?
SMTP, short for Simple Mail Transfer Protocol, is the standard protocol for email transmission on the web. It’s what mail servers use to send and receive emails on the Internet.
For example, when you send an email, your email client needs a way to upload the email to the outgoing mail server. Then, the outgoing mail server needs a way to transfer your email to the recipient’s incoming mail server.
Mail servers are much like website servers in that, while there might be a user-friendly front-facing domain name, the actual communication happens via IP addresses, like 222.501.285.45 (for more on how this happens, check out our introduction to the Domain Name System, or DNS).
A “port” is another way to help computers (like two mail servers) communicate with one another:
- An IP address identifies a computer.
- A port identifies a specific application/service running on that computer, like SMTP.
Here’s an analogy to make it a little more human-friendly:
An IP address is the physical street address of a business complex. A port is the number of a specific business in that business complex.
If you want to deliver something to that business, you can’t just address it to the business complex, you also need a way to make sure it gets to the right place inside the business complex.
IANA, the organization responsible for global IP address allocation and other tasks, is also responsible for registering port numbers for common Internet services, which includes SMTP.
Why Does Your SMTP Port Matter?
If you want to connect to an SMTP server, you need to enter both its IP address and its port number.
However, there are multiple common SMTP ports (more on this next) and not all of them work in all situations.
For example, port 25, the standard SMTP port for moving messages between mail servers, is often blocked by ISPs and cloud providers (including Google Cloud Platform, which is what Kinsta uses).
As such, if you try to connect to an SMTP server via port 25, you’ll often encounter issues because so many services block port 25.
This article was written by Matteo Duò and originally published on Blog – Kinsta Managed WordPress Hosting.