FastMail getting caught in SPAM

Has anyone else had any issues with their custom domain FastMail accounts getting caught in recipients SPAM filter? Currently I’m in a 30 trial and working with Tier 3 support on this very issue. and Exchange 365 accounts consistently filter emails as SPAM. Gmail and Google Workspace accounts inconsistently filter these same emails as SPAM. FastMail’s support states that this is normal and if the recipient removes the “junk” tag a few times MS and Google will stop filtering the email as SPAM. However, this is a new business email I’m setting up and I cannot rely on each new client to do this.

Looking through the forums here, everyone seems to have a great experience with FM. However, this issue will likely prevent me from using their services.

Has anyone else experienced something similar? I would love to use their service as I like the features but at this point, I will likely go with Exchange 365.

All email services, except for Gmail, are allowing emails to pass through correctly. Making changes to the DMARC was helpful and ultimately what allowed the emails to start showing up correctly.

Then you probably already have set up “Sender authentication” correctly?


I do not use Fastmail. Why are your emails being flagged as spam? This is something you should investigate. In order to do that, you will need your email from the spam folder of one of your recipients (the whole email file, you need the header). You have to investigate the header of your emails and look for hints what the recipient’s mail server was not fine with. And with that, you can try to mitigate the issues in question.

Sending an email from a server that is different from the server where your domain is hosted at requires some tuning in order to make sure that your emails are not being flagged as spam at many services these days.

And this is a good thing in order to protect domains from illegitimate senders. Fastmail has an article about this topic online about SPF, DKIM, DMARC, and ARC.

@rob already has posted the URL above. He was faster than me. :blush:

Unfortunately, this is something that needs some expertise, it is difficult to debug from here.

Unfortunately this was looked at by their Tier 2 and 3 support teams. I sent them the RAW Source file from the emails marked as SPAM (MS and Google). They looked through the files and determined there was not much or anything they could really do.

I would imagine it setup properly as they requested the Raw source files from the emails marked as Spam. Once they were sent, there was no mentioned of any of these being an issue.

If all of those things are fine, your emails should not be flagged as spam.

And if so, you need to investigate the header from your email that is being added by one of those servers which categorize your email as spam. Otherwise you will not learn what is causing this issue.

Check your domain using this tool:

Everything fine?

It may be obvious, but you did send them the raw source files that have been provided to you from one of the recipients who have the issue?

It does not help if you have provided the support your outgoing email from your sent objects. Because those files do not contain any headers that are of help in order to investigate this issue.

Nope! DMARC is not active. Fixing now…


I sent them the source files from my other recipient emails I used to test. I have domains with Exchange 365, Google Workspace, iCloud, Gmail, etc.

Then those headers should contain the reasons why your emails have been flagged as spam.

You may want to look inside those headers in order to see it yourself.

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Have you tried It provides quite useful insights that can help you figure out why emails might be going to spam.

I’m haven’t used this site in a while but it was very helpful on occasion.

thanks, this is very good but I have difficulty understanding the result (2nd line on the list). It has a green tick but also says policy not enabled ??

used Fastmail for a good few years with no issues that I know of. I have my main custom domain set up with all the DNS records needed dmarc etc but other domains have just the basics. None have issues.

Could the custom domain name you’re using be flagged for some obscure reason? as an example I have a client (upmarket dressage supplies) that posts shopping ads to Facebook, they consistently have ads for whips flagged as unsuitable :flushed:

Perhaps it’s the formatting/content of the email that your recipient’s SPAM filters flag, perhaps erroneously. As others have said if you inspect the headers on the emails they received, it’s surely is logged which spam checks caused “points” to “up” the SPAM score. Perhaps has nothing to do with FastMail or your domain.

thanks for the link but I still do not understand why the result said that DMARC policy not enabled but the result is DMARC Quarantine/Reject policy enabled , seems contradition to me

As far as I understand, FastMail is rather a service, than an app, right!ß
That means that the Mails are send from their IP-Adress, and not from your own.
It might be possible that their IP-Adress ended up for some reason on a Blacklist, and this could be the reason your Mail is there now, too.
I would recommend use a Tool like Mx Toolbox, already listed by @WayneG above, to check that.

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I only had to deal with this once several years ago but it appears you have a DMARC entry in your DNS records but you have not specified how to handle unauthorized emails. reject, quarantine, or do nothing

I think I read that fastmail will host your dns for free so I would think they can assist you with setting up your DNS. If not, I would check with your domain registrar. It is likely they are hosting your DNS.