Email is an extremely effective way to communicate with your customers. When done right, email can extend the conversation, earn trust and ultimately help win more business.

However, email also has the potential to be really annoying. And as any good marketer knows, the last thing you want to do is upset your customers.

Below are six mistakes marketers do to turn happy customers into crabby ones.

1. Sending a post-unsubscribe email. We’ve all been “victims” to this before. You opt-out of an email for whatever reason -- getting too many, the content is no longer relevant or you never opted in in the first place. You take the time to go through the opt-out process, as you want out. You don’t want to receive any more email from this company. Then, you get one more email restating the obvious: “This email confirms you’ve opted out.” Noooooo! One more email to read and delete. Don't be that company.

Related: 7 Myths of Email Marketing (Infographic)

Fix: Instead of sending a post-unsubscribe confirmation email, simply include that same language on the post-unsubscribe landing page.

2. Subject lines that have nothing to do with the content of the email. I’m all for getting creative with your subject lines, but there can be a fine line between being creative and being deceptive. Both can lead to an open, but the deceptive subject line -- the one not aligned in any way to the actual content of the email -- is no bueno (and could be a CAN-SPAM violation -- see #2).

Fix: Instead of irrelevant subject lines, write ones that entice someone to open the message and extend the actual content of the email.

3. Not honoring unsubscribes. You take the time to opt-out from an unwanted email. The very next day, you receive yet another email from that same company. The following week, another email. This is not only irritating but also illegal. When someone wants off of your list, it’s not only a good idea to make it easy, it’s also the law to remove them within 10 business days (see CAN-SPAM Act). I actually don’t think most marketers intentionally ignore opt outs. Instead, some have poor list management practices or unclear subscriber preferences.

Related: The Generic Email Newsletter Needs to Die

Fix: Brush up on the CAN-SPAM Act. Clean up your list management processes. Honor the unsubscribe!

4. Not optimizing for mobile. Mobile-device screens are already small. Making customers “zoom and pinch” to read the content is, well, not very fun. People, it’s 2014. The technology exists to either have a mobile version of your email (at a minimum) or a responsive designed message (ideally).

Fix: Reach out to your email / marketing automation provider and learn what mobile-optimized options they offer.

5: Making your content all about YOU. It’s not always all about you. It’s not about your company, your brand, your service or your next big thing. This is not to say the content of your email messages cannot include offers and other information about your company, but when it’s all about you, all the time, is irritating. There is no better way to turn off a customer then to talk about you.

Fix: Instead, mix up your content. Find the balance between promotional and conversational.

6: Hiding the unsubscribe button. Buried at the bottom of the email, in super-small font whose color blends into the background lies the infamous “hidden unsubscribe.” Your content is no longer relevant to me. I want off your list, yet you make it hard for me to unsubscribe. Annoying.

Fix: Marketers need to stop worrying and learn to love the unsubscribe button.

There is nothing more annoying in email marketing then, well, being annoying. Deceptive subject lines, irrelevant content, hidden unsubscribes, zooming & pinching, and more. Instead of being annoying, put yourself in the shoes of your customers. Finally, use this as your guidepost: If your email practices would annoy you, it’s quite likely it will annoy your customers.

Related: 5 Ways to Stop Your Sales-Pitch Email From Getting Trashed