How to fix SMTP sending errors
Sending messages via an SMTP server may be accompanied by errors. These errors may occur due to mail server inaccessibility, sender authentication issues, exceeded limits, mistyped email addresses, and so on.
Let's talk about common SMTP sending errors and how you can eliminate them to send emails successfully.
Error structure
Error codes consist of three digits, each with their own meaning. To understand why your email cannot be sent, you need to know the error code value.
5 first digit values in SMTP response codes
The first digit indicates whether your request was accepted and processed.
1: The server accepted your command, but no actions were taken. A confirmation message is required.
2: The server successfully completed the request without any errors.
3: The server accepted the request, but more information is required to complete it.
4: A temporary failure occurred, and the server did not accept the command. Try requesting the action again.
5: The server cannot accept your command due to a critical error.
If your error code starts with 2, it means that your command is successful; if it’s 4, there is a temporary failure; if it’s 5, there is a permanent failure. Your emails will not be sent unless you eliminate the errors.
4 second digit values in SMTP response codes
The second digit in your response code indicates the error type.
0: Syntax error.
1: Data request response.
2: Connection status.
3: Mail server or mail system status.
The last digit provides more information on the delivery status.
Error codes and descriptions
The table lists SMTP sending error codes, their messages, and more detailed explanations about each error.
The table lists sending errors you may receive when trying to connect to the SendPulse server. To see delivery errors you may receive when trying to connect to your recipient's email client server, go to the SMTP section > Delivery errors.
| Error code | Message | Description |
| 451 | 4.9.5 Sending from your account is currently limited. Please try later. | The request failed because the delivery error rate limit has been exceeded, and the emails per hour limit has been lowered.
Read more: SMTP limits after exceeding the bounce rate. |
| 451 | 4.9.5 Requested action aborted: This mail account has sent too many messages in a short amount of time. Please try later. | Local error during processing: the limits on the number of emails in your account have been exceeded.
Please wait and try again. To see your hourly and daily sending limits, go to the SMTP section in your account. |
| 501 | 5.5.2 Syntax error | Syntax error in parameters or arguments.
Make sure that commas, full stops, and other punctuation marks are spaced correctly and that your email does not contain any problematic links or attachments. |
| 501 | 5.5.2 Bad recipient address syntax | Syntax error: your recipient's email address is mistyped.
Make sure your recipients’ email addresses are correct. |
| 535 | 5.7.9 You need to confirm your email address | Authentication errors: your sender email address is not verified.
To resend your domain verification code, go to SMTP > SMTP settings > Sending domain, and select Resend code next to your domain in the drop-down menu. |
| 535 | 5.7.9 Your profile not confirmed | Authentication errors: for example, a login or password was entered incorrectly during SMTP authorization.
To view your login and password, go to SMTP > SMTP settings > Basic. |
| 550 | Service temporary unavailable | The request has not been completed because the service is temporarily unavailable.
Wait until the service is operational again. |
| 550 | 5.5.3 Too many recipients | The request has not been completed because the limits on the number of recipient email addresses are exceeded. You can add up to 50 recipients during one sendout. |
| 550 | 5.7.1 Sender domain does not match confirmed domains | The request has not been completed because the domain in the MAIL FROM SMTP session does not match the domain in the FROM header transferred after the command.
To view your verified sender domain or add a new one, go to SMTP > SMTP settings > Sending domain. |
| 552 | 5.3.4 Message exceeds fixed maximum message size | Action aborted due to exceeded email size limits.
The recommended transaction email size is 100 KB. |
| 554 | 5.7.1 Delivery not authorized | Failed to send data due to sending from an unauthorized IP address.
To view the list of authorized IP addresses or add a new one, go to SMTP > SMTP settings > Basic. |
| 554 | 5.9.1 Account expired. | Failed to transfer data due to pricing plan expiration.
To renew your pricing plan, click Rates on the left, and select a pricing plan. |
| 554 | 5.9.2 Sender domain is not valid. | Failed to transfer data due to sending via an unconfirmed sender domain or unmoderated SMTP profile.
To view your profile status, go to the SMTP section. The page should not contain a warning that your profile is under moderation or that an action is required. To view your sender email address status, go to SMTP > SMTP settings > Sending domain. |
| 554 | 5.9.3 Requested action aborted: Bandwidth Limit Exceeded. | Failed to transfer data due to exceeded traffic limits provided by the pricing plan were exceeded.
To check your account balance and get more traffic, go to the SMTP section in your account. |
| 554 | 5.9.3 Sending quota exceeded. | The limit on the number of emails has been exceeded.
To check how many emails your pricing plan allows you to send, go to the SMTP home page in your account. To send more emails, upgrade your pricing plan. In the lower-left corner, click Pricing plans, and select a pricing plan. Read also: SMTP sending limits. |
Last Updated: 28.12.2023
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