Emails going to spam


I have quite a frustrating problem with one of my customers which I can’t figure out. They are sending emails through Xojo which creates a few pdf and attaches them.

Most recipients get the emails fine, but some have the emails going to their spam folder. Similar emails would have been received without issue to the same email account prior to this and then, for no apparent reason, change. The emails pass 10/10 spam any checkers I tested with and emails sent from the customer’s outlook account go fine to the same recipient.

I wonder if any of you have had a similar problem or can suggest something that I could try to resolve this?

Thanks very much


you could look into this mails if they got a spam remark in the mail header.
maybe some customer not allow all mail domain names and block them by default.
have your sender a valid mail address?

Thanks for taking the time Markus. Yes, the email is valid. My customer is able to send emails with attachments many times a day using Outlook to the same recipient (so I think that would rule out and blocking by default), and was able to send from the Xojo program up to last week. This is around the 4th time this has happened to my customer now with different recipients.

In my experience, it’s always the mail server. I was fighting with the same issue, making sure I had everything perfect, such as SPF, DMARC, DKIM, correct return-path, reverse DNS, lots (sometimes excess) message content, company contact info… you name it. It wasn’t until I gave up and paid for an email delivery service that my messages would get through consistently. I use Postmark, costs me $10/mo, and I don’t have to worry about it.


Thanks Thom! It sounds like good advice :slight_smile: I’ll look into it. Thanks for replying

I have used them:

I did not have much luck with Mailgun or SendGrid. Too many of their servers are listed on blacklists. They don’t really care, it gives them a reason to sell you on a dedicated address, which is prohibitively expensive.

Was considering moving to SendGrid from Socketlabs so useful to know you’ve had issues with deliverability.

Thanks Michel. I see Thom would steer away, but thanks very much for your time responding

Do you do SPF?
Do you send emails over longer time with pauses?
Randomize recipients, so you don’t hit server with lots of emails quickly.
Personalize each email to be different in content?

We send thousands emails via our CURL classes and it works well.

a) You have been lucky so far.
b) Do you really know how many emails end up in the spam folder?
c) It’s not a professional way to send emails.

It’s actually your CURL plug-in I’m actually using and having the problems with Christian :flushed:

Maybe your SMTP server has not a high rating with other email servers.

The main reason for people using mailing companies is that those try to keep a high reputation for their servers.

Also check in the spam folder for why it ends there.
Spam Filters on the server add header entries for the reason.

I’m not sure if this would explain why it works sending to a company for weeks and then, suddenly doesn’t, with no significant change to the email content. Either way, it has become unreliable for me as it has occurred multiple times now

Did you get one of the emails back with headers?

e.g. did maybe the admin of that company change the spam filter to explicit catch your emails?

I’m still working on that. I’ve reached out to my customer, but, as you might imagine, it’s a little delicate, so hopefully I can shed more light on the root cause. The only problem is I can’t guarantee to my customer it doesn’t start happening again to them

Most host providers can supply a dedicated address as well, usually for a moderate price.

The problem with those stupid spam lists is that they are based on reports. Any turkey can report a domain as spam, then one has to go to every *@#£! list owner to get white listed. I know, it happened to me on the domain I used to send automated download instructions to customers.

While working on the issue I had run a few tests with Obviously I had known about emails going to spam to be curious in the first place, but these results were the real eye opener. Even when I would make progress improving deliverability, it was always temporary.

One of the issues is repeat content. In my case, all my emails are transactional. I use salted hashes to store email addresses, so I cannot send marketing emails even if I wanted to. I send exactly three kinds emails: verification code, welcome, and gift codes. That’s it. You can imagine that something like verification code emails don’t have a lot of content. So I would do things like include the latest news from the website towards the bottom to add more varied content.

The trouble is scale. Google and Outlook receive so many emails that no matter what I did, within a few weeks they would be flagging my emails again. They would see that just about every email from my server looks similar. And since the two of them receive the majority of the world’s emails, they’d have lots of data to work on.

Once I gave up and switched to Postmark, that was the first time I had seen a 100% score from glockapps. For the record, when I tried such a test with MailGun and SendGrid, I got worse scores than my own server.

On a side note, I’ve always run my own mail server, including for incoming. I used yahoo like 20 years ago, but since then I’ve done it myself. I recently decided I hate messing with it all the time. I ended up switching to Google Workspace, and my inbound email is so much nicer. The main thing is spam. Back to the scale I was talking about, Google has so much data that they can catch spam WAY better than SpamAssassin could ever hope to. The other stuff is largely irrelevant though, so I’m really just paying for reliable spam filtering.

Sure. I’ve had a dedicated address for a long damn time. That can be counterproductive though, as odd as it sounds. As mentioned in my other reply, nearly every email from my server is very similar. This is where a dedicated address is working against me. Using a third party, they have more servers, more users, and more customers. The emails their servers send will naturally be more varied. Postmark actively works to keep their servers off blacklists. When I reported the numerous MailGun servers I had found on blacklists, they of course told me they would take care of it, but then gave me the song and dance about upgrading to a dedicated. Which wouldn’t necessarily help my deliverability, since I already had my own.

MailGun and SendGrid are huge. They didn’t get that way by being bad at their job. But I think they’ve become so successful that they’ve become complacent. I get the impression that they don’t really care about deliverability any more. That’s not their goal. Their goal is money. I mean, let’s be real, money is the goal of every business. But when deliverability tests for both of them come out worse than my own server, that’s pretty telling. That’s why I like Postmark. Small team (usually the same person answers my emails each time) and seems to truly care about getting my emails delivered.

Thom. Thanks for all the advice and sharing your experience. Obviously, I’d prefer to keep the emailing solution “in-house”, but it will be next week before I receive the spam email with the spam header (I’m living in Ireland where we have a holiday for St. Patrick’s Day and our government have given us a second one tomorrow for COVID).

I am playing with Postmark at the moment, as I expect it will be they way I go in the end, but it looks like I need to verify every sending domain with access having them to access their web server… is this the case? It would make roll out of new installations more tedious…