Outlook Error Codes

How to Fix Outlook SMTP Submission Failed Error 501

John Wilson Oct 9, 2026 870 views

Question details

The user is unable to send outgoing emails in Microsoft Outlook due to an SMTP submission failure returning error 501.

How to Fix Outlook SMTP Submission Failed with Error 501

Product: Microsoft Outlook
Device & OS: not provided
Scenario: Sending outgoing emails using an IMAP account setup.
Observed behavior: Outgoing messages are undeliverable. The server returns error 501 on port 25, stating that the parameters or arguments contain a syntax error.

Before you start

Gather your exact email provider configuration settings, specifically the outgoing SMTP server address, supported port numbers (like 587 or 465), and encryption method, before making changes to your Outlook account.

Solution 1Recommended

Update Outgoing Server Port and Encryption Settings

Switching from the commonly blocked port 25 to an authenticated submission port like 587 with STARTTLS often resolves SMTP syntax and delivery errors.

Internet Service Providers (ISPs) frequently block port 25 to prevent spam. Modifying your advanced account settings to use your provider's authenticated port is the most common fix for error 501.

Access Account Settings

Launch Microsoft Outlook, click on the 'File' tab in the top-left corner, click 'Account Settings', and then select 'Account Settings' again from the dropdown menu.

Select the Affected Email

Under the 'Email' tab, find and double-click the IMAP email account that is experiencing the SMTP submission error.

Open Advanced Settings

In the account properties window, click on the 'More Settings' button in the lower-right corner, then navigate to the 'Advanced' tab.

Change Port and Encryption

Locate the 'Outgoing server (SMTP)' field and change the port number from 25 to 587. From the 'Use the following type of encrypted connection' dropdown list, select 'STARTTLS' (or 'TLS').

Save and Test

Click 'OK' to close the advanced settings, then click 'Next' in the main window to let Outlook test the new configuration. Once the test passes, click 'Finish'.

Update Outgoing Server Port and Encryption Settings

Verify ISP Settings: If port 587 with STARTTLS does not work, consult your Internet Service Provider's documentation, as they may require port 465 with SSL/TLS encryption instead.

Solution 2

Manually Recreate the IMAP Email Profile

If Outlook's automatic setup fails to apply the correct parameters, creating a new profile manually ensures all server requirements are strictly met.

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Frequently Asked Questions

What does SMTP Error 501 mean in Outlook?

SMTP Error 501 indicates a syntax error in the parameters or arguments sent to the email server. This usually happens when Outlook attempts to connect using incorrect port settings, unsupported encryption types, or when an email address is improperly formatted.

Why is port 25 blocked for outgoing emails?

Many Internet Service Providers (ISPs) actively block port 25 by default. This is a standard security measure designed to prevent spam, malware, and unauthorized servers from sending unauthenticated emails across their networks.

How do I find the correct SMTP settings for my email provider?

You can typically find the correct IMAP/SMTP server addresses, port numbers, and encryption methods by visiting your email provider's official support website or by searching for '[Your Provider Name] IMAP SMTP settings'.

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