SMTP, or Simple Mail Transfer Protocol, is a way for servers to send email to recipients over the in...ternet. Although SMTP is now an ‘old’ protocol, having been developed in the 1970s and claiming its original definition in 1982, it’s still very much in use today.

Most internet users will have come across the term ‘SMTP’ when entering server details into email software. This method of using SMTP is slightly different; it’s only used for sending messages from the software to the server. Receiving email messages on this local level is handled by either POP, IMAP or some other protocol such as those employed by Microsoft Exchange.

On a wider scale, SMTP delivers messages by determining the recipient domain’s MX record. The MX record can usually be changed in the domain registrar’s control panel, allowing you to re-route emails to your domain through an alternative server. An MX entry must follow a certain format, and care is needed not to set it incorrectly because it will cause emails to be undelivered.

In the past, SMTP servers have been offered on an open basis, meaning anyone could use them for sending email. The first spam message is thought to have been sent in 1978 before the implementation of SMTP, and there are reports of ‘unwanted’ mass emails dating back to 1971. An open SMTP server is a target for spammers looking for an untraceable way to send email. Many providers now restrict the use of SMTP to their own customers, ensuring that any email sent through their SMTP service comes from a traceable source. Some servers will require authentication in addition to this, or will restrict the use of the SMTP server to people within a defined IP range. Any server that does not have some kind of restriction on its use will be quickly blacklisted by ISPs, largely due to a high likelihood that it will be used for sending large quantities of spam email. Anyone setting up an SMTP server needs to ensure it is properly configured and secured to avoid being accidentally blacklisted.

In addition, some providers will place limits on the size of emails that can be transmitted. Limits on message size are rising slowly with the advent of cloud email hosting, increasingly more complex multimedia attachments and faster internet connections. Many users choose to use online file hosting or storage services to get around file size restrictions via SMTP.

SMTP hosting is often included in your hosting plan

There’s no need to look for a separate solution if you need SMTP hosting. Many providers will give you access to their SMTP servers with any web hosting package. Even the most basic shared web hosting accounts usually have some form of SMTP relay included, and reseller hosting or dedicated hosting will give you more options to customise that provision. For example, if you resell web space to your clients, you may wish to offer them SMTP, POP or IMAP server names that match their own domain. Using the SMTP provision with your ISP gets around the issue of having to comply with complex rules and security or fretting over port settings and authentication.

SMTP options are normally configured in your control panel. On Linux, this is usually CPanel or Plesk. Once your SMTP service is configured, you don’t need to touch it again - unless you switch hosts in the future.

SMTP helps you to look professional

SMTP servers often only permit connections from paying customers. Restricting the people who can use SMTP is a way to prevent anonymous users from using SMTP to send spam emails. If you or your client is signed up to a monthly plan with an ISP, you may have access to their SMTP servers to send messages, but it doesn’t always give the best impression to clients.

If you don’t have an ISP, you may find you need to pay for an SMTP service or hosting plan, but this gives you the advantage of using your own domain for email - a much tidier and more professional solution. It also means you have more control over your email provision, and any limits on file sizes and file types are likely to be more relaxed.

A note for those who send newsletters

If you send newsletters, it’s best not to rely on your personal or business ISP for SMTP provision. You may not be permitted to send large quantities of email, and you may be at the mercy of your ISP’s technical support helpline if any problems arise. Your messages may also be mis-identified as spam, or your ISP could block port 25 entirely.

Your own host is more likely to accommodate this type of mailing, but if in doubt, specialist mailing list applications can be used. One of these, PHPlist, is often included in Fantastico on Linux servers, giving you an easy one-click installation option for bulk emailing; more elegant solutions can be found online.

Regardless of how you send out your newsletters, you must always take care to comply with any anti-spam policies. One common requirement is the inclusion of a clear ‘Unsubscribe’ link in the header or footer of every email you send out: failure to include this will flag your mailouts as spam, and your account will be suspended.

Always make sure your subscribers have opted-in voluntarily, and restrict the speed that messages are sent. Most hosts will begin to worry if you’re sending out more than 200 emails per hour.

Check your SMTP mailbox provision

Cheaper plans may place restrictions on the amount of server space you can use for emails, files and bandwidth. Check the SMTP provision on your chosen hosting plan and make sure there is enough capacity for you and your clients. Some hosts offer extras, such as webmail applications, or easy set-up files for programs such as Microsoft Outlook that automatically configure mailboxes for you. If you support a lot of clients, these features could save you some time and hassle in the long run.