Let's say you send an email, only to have the recipient discover it hours later in their Spam folder.
Spam filtering is performed by email providers to protect their recipients from unsolicited or malicious emails. No spam filters are perfect, and they may cause your legitimate email to be marked as spam.
It's often difficult to know why a message was filtered as spam. In this help page, we'll cover the most common scenarios that might cause an email to be marked as spam on the recipient's side.
- The email is considered bulk sending
- Something in the email's content is considered suspicious
- The email is not properly authenticated
- The email address has poor domain reputation
- Contact support
The email is considered bulk sending
Sending bulk mail can increase the chances of your messages being marked as spam. Email providers sometimes apply stricter requirements for bulk senders, so it is generally better to use a dedicated bulk mailing service.
If your workflow involves sending marketing, newsletter, transactional, or notification emails, we ask that you please use a service dedicated to bulk mailing. Sending bulk emails is not permitted under our Terms of Service.
Something in the email's content is considered suspicious
One of the factors an email provider considers while deciding whether an email is spam is its content. Excessive use of words seen in promotional emails, links to websites or domains with a poor reputation, and signatures containing multiple links are some of the common reasons why an email may be marked as spam.
If you suspect that your email's content may be considered suspicious, you can test this by sending a plain-text email with a short sentence. If the email doesn’t go to the recipient's spam folder, the problem is almost certainly the content of the email you sent earlier.
The email is not properly authenticated
Email authentication is a set of protocols that verifies the legitimacy of the email sender, helping to control and recognize email spoofing. It uses existing standards like SPF, DKIM, and DMARC to confirm that an email is genuinely from a sender authorized to use the domain it claims to be from. If the domain has not been properly set up, mail providers may mark your email as spam.
If you're using a Fastmail domain, we will take care of the necessary DNS records to have the email sent out with proper authentication.
If you're sending emails from a custom domain, make sure that your domain's DNS records are configured correctly to send emails. You can check if the SPF and DKIM configurations are correct by opening your domain from the Settings → Domains screen.
The email address has poor domain reputation
The recipient’s email provider may mark an email as spam if it is coming from a domain with a low reputation. If your domain is newly registered, this can cause it to be considered low reputation. Your domain could also have a low reputation if it has been reported for spam too many times, or if it is on a blacklist.
If you suspect that your domain’s reputation is causing the issue, you can test this by sending the same email again, but this time from an alias at a Fastmail domain instead of your custom domain. If the email doesn't go to the recipient's spam folder, the problem is likely the domain's reputation.
Domain reputation specific to an email provider
If you notice that emails addressed to only a particular email provider are being marked as spam (e.g. every message you send to someone using Outlook goes to their spam folder), it usually indicates that the domain has been blacklisted by that email provider.
It may be helpful to ask your contacts who use the same email provider to mark your emails as "not spam," which could help increase the reputation of your domain at that provider.
Domain reputation specific to a single recipient
If your emails are only being filtered as spam when sent to a specific person, it could be caused by a specific rule, setting, or filter on that recipient's account. You can ask the recipient to:
- Review their mailbox rules or filters to see if emails from your address or domain are being asked to be marked as spam.
- Add your email address or domain to their Safe Senders/Allowed Senders list.
- Contact their email administrator if they are a part of an organization to verify that they aren’t filtering the your address or domain.
Contact support
If you’re unable to narrow down the issue, ask the recipient for the full headers of the email that was marked as spam. These headers may contain information about why an email was marked as spam.
Contact our support team with these headers and the details of the troubleshooting steps you’ve already performed, and we can look into this further.