how to avoid having your email accidentally flagged as spam

This is not the kind of do-not list you may think it is. It's not something where I say, "you must only send email in a very specific way" and blah blah blah. I'm not telling anybody to follow Netiquette Guidelines from 1995, because screw that (and you will be amazed at how dry and restrictive that is).

Instead, this is a do-not list to use when sending email to anybody. I guarantee that if you follow what this list says, the likelihood of your emails being accidentally flagged as spam will decrease dramatically, if not completely.

Ready? Here we go.

Do not rapid-fire send emails.

If you're sending more than 1 email every 2 minutes, you are rapid-fire sending.

Sometimes you may have a bunch of separate emails to send to different people. If you compose those messages and then click-click-click like crazy to send them all out, two things will happen.

First, the sending email server (the one you're using) may slam the brakes and not even allow you to send the messages.

Second, the receiving email server(s) may flag the messages being received as spam; this is especially true if two or more of the recipients have the same domain, such as bob@example.com and alice@example.com.

If you routinely send a lot of emails, spread out when they're sent. This can be done manually, or by using a Thunderbird add-on called Send Later, or in Linux with mutt using at (e.g. echo 'echo "message body here" | mutt -s "subject here" recipient@email.dom' | at now + 5 minutes for sending 5 minutes from now), or whatever. You have options.

Do not use link shorteners

This is when you take a long web address and shorten it using a link shortening service. Instead of https://www.example.com/whatever, it's https://f.u/dick or some such. Spammers use these a lot, which is the reason why you shouldn't in your emails.

Do not carbon-copy and/or blind-carbon-copy a shitload of recipients

Hardly anybody uses Cc or Bcc outside of an office these days, but if you're thinking about using it, don't. This can get your message accidentally flagged as spam just as much as rapid-fire sending does.

Do not attach anything

ZIP, RAR, 7Z, DOC, DOCX, XLS, PDF, whatever. Attach nothing.

While true you may receive emails from official offices with one of these attachment types (usually PDF), that doesn't mean it's OK for you to send an email with one. If you do, your message will most likely be insta-flagged as spam.

Are JPG images safe to attach? Not really.

Some receiving email servers are unbelievably restrictive to the point where if any attachment is seen in a message, it will flag the message as spam.

If you absolutely have to attach images, only have them as JPG, and keep the total size of your entire email under 5 megabytes. Yes, MB and not GB. I know, I know.. you may have sent 10MB or even 30MB emails and gotten away with it before. Eventually, you won't, and the receiving email server will either a) spit back an "undeliverable" message, or b) the receiving server will flag your message as spam, or worse yet "blackhole" the message, not ever tell you there was a problem, and the recipient never gets the email.

Do not use an email signature

You get a pass on this if using office email system and it forces one of these whether you want it or not.

For your personal email however, ditch this if you are using one. In the stupid ways that some receiving email server filters are configured, your signature can actually get your email flagged as spam.

A genuinely stupid signature is anything with an image. This means you're either attaching a file to every single email you send (dumb), or every email you send tries to pull an image from the internet to display (seriously dumb).

Does that mean text-only signatures are safe? No! Your "creativity" with your email signature may match a pattern that receiving mail servers identify as, you guessed it, spam.

The general rule of thumb is this: Treat every email you send or reply to like you would a text message on your phone. No signature, and no text formatting. Speaking of which...

Do not use formatted text in your email

This is anything with differing font sizes, bold/italicized/underlined/colored crap, and so on.

Any time you do this, your email contains HTML formatting. This is a bad idea not only because receiving email servers can flag that as spam, but there are also tons of email readers both client and web-based that strip all that formatting right out.

Formatting text in email is a total waste of time, so it's not even worth the bother.

Quick blast to the past:

The worst that formatted email ever got was back in the late '90s. In the absolute worst case scenario, there were morons who would do the following:

• Use every kind of text formatting they could. Use of Comic Sans, different font sizing, bold/italic/underline, different colors, all of it.
• Use of a giant email signature with an animated GIF image that in many instances was at least 300% bigger than the content of the message itself.
• Use of an animated background "wallpaper" GIF image (much like the stars animation you're seeing here).
• Have some images attached and others pulled from internet web sites. Yes, in the same message.
• Have a MIDI music file start playing automatically when you opened the email. Yes, this really happened.

Email clients of the time had a thing called Stationary that gave the user the ability to custom craft a whole lot of garbage, and so they did. All it did was put gobs of poorly coded HTML crap into email messages.

Understand that "private email" does not guarantee anything

Not with avoiding having your messages accidentally flagged as spam, anyway.

At the time I write this in early 2026, "private email" services have been gaining traction for a few years now. People are getting wise that the Big Email Provider account they have may be selling off all their personal data, so they switch over to a "private email" service.

That's all well and good, but if you're still rapid-fire sending emails, using link shorteners, Cc and Bcc'ing everybody, attaching files left and right, using a dopey signature, and formatting the crap out of all your messages, well then... nothing will improve, will it?

The best thing you can do is what I said earlier. Every time you compose a message, whether new or as a reply, treat it the same you would as a text message on your phone. Do that, and the likelihood of your message being delivered successfully increases dramatically.

~ ~ ~

Would "business class" email help?

Short answer:

Only if you can switch mail hosts whenever you want but still keep the same email address.

Long answer:

You have most likely seen some of those "private email" providers offering the custom domain option, like you@example.com, where example.com is whatever dot-com or dot-whatever you bought.

When you own the domain, you can host your email at any mail host provider you want, and switch providers at any time.

What this means is that if for whatever reason you're having problems with email being accidentally flagged as spam, switching mail host providers may solve that problem. And since you own your own domain, you're not locked in. For example, if you have an @yahoo.com email address, that's locked. All mail incoming and outgoing is through yahoo.com servers and you have no choice otherwise. But with your own domain, you do have choice. Your email address stays the same, and you can switch mail host providers whenever you want.

Domains aren't free and neither is email hosting, but at the same time it's not terribly expensive either. Do a search for 'email hosting' and you'll find a bunch. Also do a search for 'domain registration', because you may find a registrar that has a register-and-mail-hosting plan that suits what you're looking for.

"I don't want to do any of that and keep what I have."

Fine, then. Follow what I said above and your emails will go through. Don't rapid-fire, don't use shortened links, don't Cc nor Bcc, don't attach anything, don't use an email signature, don't use formatted text.