Last updated: 2 March 2022

As you no doubt know all too well, spam is a hugely annoying issue. The majority of emails are spam, and various solutions have been invented to try to weed out junk emails before they reach your inbox. For the most part, these solutions work pretty well. The majority of spam is blocked, without the need for you to do anything. However, no anti-spam solution is perfect. Some spam email filter through the net, and some genuine emails are incorrectly marked as spam.

Emails that are marked as “potential spam” are often delivered to a recipient’s junk folder. And, if a server is sure an email is spam then it will typically reject the email. In most cases the sender then gets a bounce email. The email contains information about why the email was rejected.

There are various things you can do to prevent your emails are marked as spam. The main things to consider are DNS records, IP blocks and the emails themselves.


The most common reason for email delivery issues are incorrect or missing DNS records. If you are not familiar with DNS then it is easiest to contact us about emails delivered to spam folders. We are happy to check the DNS for your domain.

In general, your domain needs to have at least a valid SPF record. The record tells receiving mail servers which IP addresses are allowed to send mail for your domain. If the sender’s IP address is authorised then the receiving mail server can be fairly confident that the incoming email is legitimate. Of course, the reverse is also true: if the sender’s IP address is not authorised then the email is often marked as “potential spam”.

SPF records are not a perfect solution, and we therefore got a similar type of DNS record: DKIM. With DKIM, outgoing emails are signed, and receiving mail servers can check the signature using the DKIM record. If the signature checks out then the email was sent from an authorised mail server.

And finally, DMARC records give you the option to explicitly tell receiving mail servers what they should do if the SPF and/or DKIM check fails. This can be useful, as SPF and DKIM records don’t tell receiving mail servers what they should do if a check fails.

If we are managing the DNS for your domain then you should already have an SPF and DKIM record – they are automatically set up when a hosting package is created. However, it may be that the DNS for your domain is managed elsewhere or that the records have been deleted or changed incorrectly. The above-linked page about SPF record contains various examples of SPF records.

Mail server blocks

Receiving mail servers often check the sender’s IP address against block lists such as SORBS and Spamhaus. A mail server’s IP address is typically added to a block list when a large amount of spam was sent from the server.

Such spam issues most commonly happen with IMAP/POP3 accounts on shared hosting servers. These servers host many websites and email addresses, which all sent emails from the same IP address. If one email account (or website) is compromised and starts sending spam then the server’s IP address is likely to be added to block lists very quickly. Unfortunately, that affects everybody sending emails from the server.

We obviously try to prevent this from happening. For instance, we try to force users to use strong passwords, and our firewall blocks an IP address when there are five failed login attempts in a short period of time (which stops brute-force attacks on email accounts). We also monitor SMTP activity, as well as all major block lists. Still, most shared servers suffer the odd spam issue. In those cases we resolve the issue and request the removal of the block. The process may take a day or so.

If email is critical for you then you should consider if hosting your email on a shared server is the best solution. Our Office 365 packages might be more suitable. Or, our premium servers could be a good alternative.

Home IP blocks

The issue may also be that your home IP address is on a block list. You can check if that is the case by finding your IP address and checking the IP against common block lists. You can check a large number of block lists via websites such as MxToolbox.

The most common reason for home IP blocks is that you haven’t enabled SMTP authentication in your email client. In that case you simply need to change the authentication setting in your email client.

Another possible reason is that your ISP requires you to send emails via its mail server. This is the case with BT Retail customers, for instance. In such cases your ISP should be able to help find a solution.

Marketing emails

The issue may also be the email itself. For instance, marketing emails are often marked as spam. In general, you should not send marketing emails and newsletters from a shared server. It is better to use an email marketing service instead. Such services have well-established policies for ensuring that recipients have opted in to receiving emails, and people on your list can easily unsubscribe. Also, recipients can complain about emails, and the service provider can suspend the account of users who repeatedly abuse the service. You get none of that when you send marketing emails via an email client or script. As a result, receiving mail servers are unlikely to trust such emails.

A more tricky area are emails that are not quite marketing. For instance, you may have an online shop that sends emails to people who added an item to their basket but didn’t proceed to the checkout. Such emails may be marked as spam, and there is a good reason for that. The emails will be generic, aim to sell something and, in most cases, the recipient is unlikely to be keen on your email.

All major email providers, such as Gmail and Hotmail, publish (bulk) sender guidelines. If you are sending marketing emails or newsletters, make sure you are familiar with the guidelines and resolve any potential issues. A good starting point are Gmail’s guidelines.

And finally, a really useful tool for checking if there are any issues with emails you send is The tool is mainly useful for analysing if there are any issues with the content of your emails (though it does a bunch of other checks as well).