If you send bulk emails, you may face the problem of delivery errors. Knowing the reasons will help you cope with it and increase conversions. After the registration in SendPulse, you're welcome to monitor your campaign statistics including the errors. Keep on reading the article to discover its causes and ways to avoid.

SMTP error 501

Error 501

HTTP 501

501 Not Implemented

HTTP Error 501 Not implemented

The server either does not recognize the request method, or it lacks the ability to fulfill the request.

Command is correct and recognised, but the parameters were invalid. You may receive this error when sending to invalid email addresses or to an invalid domain name. Also, it may be caused by drops in communication and problems with antivirus settings.

SMTP error 510

Address rejected

Bad Email Address

Sender's mail server generates this code. It means that email does not exist or was misspelled. Check your recipients' emails and correct the typos.

SMTP error 513

SMTP error 501 5.1.3 Invalid address

SMTP error 501 5.1.3 Bad recipient address syntax

Address type is incorrect, there may be typos. You could have copied or pasted an address from a website wrongly. If you have checked all the addresses, and still receive this error, the server needs an authentication.

SMTP error 515

Destination mailbox address invalid

An email address you want to send to may not exist or there may be typos. Check all the emails for any misspellings.

SMTP error 530

530 Authentication is required

SMTP error 530: The message cannot be delivered due to a configuration error on the server. Please contact your Administrator.

You can receive this error due to several reasons:

  • You may have an invalid recipient's address, containing misspellings; or it simply does not exist.
  • A recipient's server could have blacklisted yours only.
  • Invalid authentication. Configure the settings.

SMTP error 553

553 Your email address is denied.

553 sorry, this recipient doesn't exist.

553 #5.1.8 Domain of a sender's address does not exist

553 5.3.0 ... Address does not exist

553 message blocked, you are not authorized to send mail, authentication is required.

You can receive this error if the email address you send to does not exist, or there may be typos, so check. Or, you try to send email using an SMTP of an ISP with no authentication and no connection to the internet via this ISP's service.

Why do your mailing lists contain invalid email addresses?

Invalid email addresses in your list may be spam traps.

Spam traps are the email addresses used to catch spam senders. They are usually created by inbox or blacklist providers to maintain anti-spam policy and healthy mailing lists. If you send emails to spam traps, you risk to be blacklisted, since it means that you take no care about your mailing list hygiene. Thus, you can get a spam sender reputation.

How can spam traps occur in your mailing list?

1. Recycled email addresses

These are real but abandoned email addresses. Internet service provides deactivate addresses after some period of being inactive. Sometimes, they use them like spam traps to identify spammers. 

2. Pristine email addresses

These emails are never used by people. They are placed on public websites but hidden in the code. Their aim is to reveal bad practices of email list growing such as website scrapping. 

3. Old and inactive subscribers

Your mailing list may include the same email addresses that you’ve collected at the beginning of your business. That’s why some of them can be unengaged. Sending to inactive subscribers, you’ll get bounces.

4. Misspelled email addresses

People can give you an address with the typos both deliberately and unintentionally. In the first case, they can fill a form that needs an email but they don’t want to share it, thus they type anything that comes to their mind. Certainly, such an address will be fake. In the second case, it’s just a misprint. Still, you have to take steps to avoid spam traps.

How to avoid sending emails to spam traps?

1. Contact inactive subscribers

Send an email to subscribers who have not been active for 1 year, for example. Just ask if they are still interested in you. If not – give them a chance to unsubscribe.

2. Make use of double opt-in

Double-opt in is a great practice of growing an email list of interested and engaged subscribers. Using this method, users are to express their wish to subscribe via the confirmation email. Thus, you will have fewer subscribers, but the mailing list quality is more important, isn’t it?

3. Check new email addresses

Use a validation tool to find fake and misspelt email addresses. 

4. Never buy mailing lists

The most obvious advice ever, but it works. A bought email list is the collection of everything that looks like a real email address. Surely, they will never bring you engagement.

Besides, adding a mailing list to SendPulse, you’ll have to prove that you have a permission to email the users. This is the way an email service prevents sending spam.

5. Monitor campaign statistics

After sending an email campaign in SendPulse, go to Reports and check its performance.

Delivery errors statistics report

In "Error statistics" you'll discover the number and type of email delivery errors. They'll help to:

  • clean your mailing list
  • keep sender reputation high
  • send campaigns to engaged subscribers only
  • pay an email service for active subscribers

If your mailing list has up to 2,500 active subscribers, enjoy the benefits of our free pricing plan!

Send 15,000 emails every month at no cost. Make use of personalization, segmentation, ready-made email templates, and subscription forms to make email marketing yield additional income.

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