SMTP Error Code 451

SMTP Error Code 451 - Quick Fix

The SMTP Error Code 451 generally occurs when the attachment limit of your email account is exceeded. Sometimes, it can happen if the SMTP server settings are incorrect. If you are using Outlook 2016 and getting the SMTP error code 451, follow the troubleshooting steps given below.

Solution 1: Modify Default Attachment Size

  • Step 1:If you have already opened Outlook, close it.
  • Step 2:Open the Run command box by pressing the Windows + R shortcut keys.
  • Step 3:Type regedit.exe in the Run dialog box and click OK to open the Registry Editor.
  • Step 4:Go to any one of the following file paths in the Registry Editor window.
  • Step 5:Right-click the registry subkey and select the option to modify the registry data.
  • Step 6:Enter DWORD in the Value type field.
  • Step 7:Type “MaximumAttachmentSize as your Value name.
  • Step 8:To configure no limits for attachments, specify a value of zero in the Value data field.
  • Step 9:Exit the Registry Editor window and launch the Outlook app.
  • Step 10:Send a test email from Outlook and check if the SMTP error code 451 is resolved.
  • Step 11:If the SMTP Error Code 451 persists, carry out the next solution.

Solution 2: Check SMTP Server Settings

  • Step 1:Launch Microsoft Outlook 2016 and click on the File tab.
  • Step 2:Select the Info option from the left-side panel.
  • Step 3:Click on Account Settings twice.
  • Step 4:In the Account Settings window, click the Email tab and select your email account from the available list.
  • Step 5:Click the Change tab to open the POP and IMAP Account Settings page.
  • Step 6:Check the email account details in the User Information and Logon Information sections.
  • Step 7:Under Server Information, check if you have entered the correct outgoing mail server name.
  • Step 8:Click on More Settings to open the Internet Email Settings window.
  • Step 9:In the Outgoing Server tab, ensure that the My outgoing server (SMTP) requires authentication checkbox is selected.
  • Step 10:Also, check if the Use same settings as my incoming mail server option is selected.
  • Step 11:In the Advanced tab, check if the server port numbers are correct in the Incoming server (IMAP) and Outgoing server (SMTP) sections.
  • Step 12:Ensure that you have selected the correct security types from the available drop-down menus.
  • Step 13:Click OK and check the configured settings by clicking the Test Account Settings button.
  • Step 14:Once the verification is complete, click Next and return to the main page of the Outlook app.
  • Step 15:Try composing an email from your account and check if the SMTP error code 451 is resolved.

In case you need assistance in resolving the SMTP Error Code 451 issues, click the Call button on this page and contact our technical experts.

Related Searches

How To Encrypt Email?

How To Encrypt Email?

In order to prevent third parties from reading your mail content, email encryption is done, which is basically digitizing the information within. 

How To Stop Spam Emails?

How To Stop Spam Emails?

There are not many ways to prevent spam from piling up in your Inbox. Here’s how you can filter out most of them.

Fix AT&T Email Error

Fix AT&T Email Error 0x800CCC0F

AT&T Email error 0x800CCC0F occurs when mails are not being sent or received through AT&T services. Due to the technical glitches causing it, many email functions are disabled. The computer’s Operating System might get frozen.

How To Delete All Emails In Gmail?

How To Delete All Emails In Gmail?

Open the Gmail app.Select the inbox tab you want to delete.You’ll find the Empty Box button over the Compose button.