Computing

Port and server information for email accounts.

Email: It's been around for decades, and people are still confused about how it works--and for good reason. Setting up and troubleshooting an email account can be an irritating venture. Recently, we wrote articles on email problems in which commenters

Email: It's been around for decades, and people are still confused about how it works--and for good reason. Setting up and troubleshooting an email account can be an irritating venture. Recently, we wrote articles on email problems in which commenters have been curious about the setup for various ports and other aspects of email accounts.

MacFixIt reader "Robert G Boulay" asks:

"You mention TCP port number. I've had problems with those. Can someone explain these cryptic numbers (25, 110, etc.) and what we should do about choosing the right one?"

Let's take a look at the common email account types and setup options, which should provide some insight as to what is going on with your email accounts.

IMAP versus POP

There are many types of email accounts out there, but the primary types are IMAP (Internet Message Access Protocol) and POP (Post Office Protocol), though Microsoft Exchange is another common one. The main difference between these two types of accounts is how the server manages the files. With POP accounts, only new messages are downloaded and are then removed from the server after a set amount of time. As such, this does not let you easily manage emails from multiple computers.

IMAP, on the other hand, synchronizes local mailboxes with those on the server, and as such let you manage your email from multiple email clients. With IMAP, you receive old messages as well as new and unread ones when you check your email. The drawback to IMAP is since all email is managed on the server, you may fill up your email account very quickly; however, many ISPs and email providers are compensating by allocating massive amounts of storage to email accounts (Gmail and MobileMe, for instance, which allow for gigabytes of additional space to be dedicated to the account), unlike years ago when a common disk quota for email was less than 10MB.

While advancements in these protocols have blended some of their features together, these are the main differences that still hold true for the most part.

SMTP servers

"Simple Mail Transfer Protocol" servers are your outgoing server. These are the ones you connect to in order to send a message to another person. While your main email server is just a mailbox of sorts, the SMTP server is the actual post office, using a simple protocol to establish a connection with an email "mailbox" server and deposit a message in a designated mailbox.

In most setups, you will have your main email server along with an SMTP server from the same provider. While for most email accounts you should be able to send email using any SMTP server that you can access, sometimes there are restrictions for which email addresses are accepted for sending with an SMTP server. Therefore, check with your internet or email provider to see if your SMTP server can be used with your email account.

SSL

In last week's MacFixIt Answers article, we discussed how SSL works. This encryption technology is widely implemented in email, and we recommend you enable it whenever possible. SSL will ensure third-party servers cannot intercept your email messages when they're in transit from your client to the SMTP server, or from your email server to your client.

Port configurations

The various options for incoming and outgoing email servers, as well as secure encryption all require the user to set up various "ports" in the email clients being used. So what exactly is a "port"?

In a typical TCP connection, a server (email server) has an IP address and runs programs that host services, which allow for clients to connect and run some task, such as checking email. Since one server can run multiple network services (Web, email, file sharing, and so on), it needs a way to distinguish the network traffic for these services even though they all connect with the same IP address, and ports are the way to do this. The basics for how it works is a standard TCP packet is tagged by the sending computer (your desktop) with a port number, and the server receives that port number and sends the tagged data to the service it is running that is responsible for handling it. As such, the same computer can host a Web site (port 80) and an IMAP email server (ports 143 and 993), at the same time without any traffic interference.

Here are some common ports for a variety of services used by Apple's programs and devices. Many of these are industry standards, but some are used specifically for Apple's services: http://support.apple.com/kb/TS1629

One thing to keep in mind, is that while the ports used are common and standardized, their implementation is up to the server administrator. For instance, while a standard Web server runs on port 80, a server admin can change their setup to receive Web traffic over port 99, or port 102 if they so choose. As such, Web clients trying to connect will receive an error if they use the default port 80 when connecting to these servers. This same situation applies to any network service, including email, and while it is rare that a server admin will change ports to unconventional ones, it is a possibility.

With that being said, here is the standard setup for the ports to use with email accounts:

Incoming email server:
IMAP, non-SSL: 143
IMAP, SSL: 993
POP, non-SSL: 110
POP, SSL: 995

Outgoing (SMTP) email server:
non-SSL: 25
SSL: 587 or 465

While these ports are the standard ones for email setups, they can be used in unconventional ways by system administrators, in which case you will need to troubleshoot the connection.

Troubleshooting

The best way to troubleshoot and email problem is to contact your administrator and get the exact ports to use for the type of connection you are meaning to establish. Let your administrator know if you want to use SSL on either or both of the incoming and outgoing servers, and see what ports are designated for those connections.

Additionally, if you are having troubles with your email account, the problem may be with the server, and contacting the administrator is the fastest way to determine if this is the cause. Optionally, many service providers have support websites in which announcements will be made about service outages.

An alternative is to methodically try each port in various circumstances. For institutions that have firewalls and other network setups, many times they will change the ports to manage network policies. For instance, a workplace may accept SSL over port 25 to agree with firewall policies, in which case connecting to the SMTP server from outside of the network would require you to have SSL enabled and the port set to 25, which is the default for non-SSL connections.

The key to methodical experimentation is to change one setting at a time, and write down which ports worked and which ones didn't. Be sure you've appropriately changed the settings for the desired account (which can be easily mistaken if you've got multiple accounts set up in your email program), and you may also optionally try relaunching your email client after each setting change.

Resources
  • MacFixIt Answers article
  • http://support.apple.com/k...
  • More from Late-Breakers