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Failed Connection, Relay, and Socket Errors - SMTP Server Settings
12-30-2010, 06:04 PM
Post: #1
Failed Connection, Relay, and Socket Errors - SMTP Server Settings
  'Failed Connection', 'Socket Error', 550 & 553 Relay, and "RCPT' errors usually indicate that your outgoing SMTP mail server is not specified correctly in Mach5 Mailer. Before troubleshooting, we recommend you update to Mach5 Mailer 4.5 if you have not already. Mailer 4.5 is a free upgrade for all Mailer 4.x license holders and adds SMTP Auto Detection which greatly simplifies SMTP configuration. You can download Mach5 Mailer 4.5 from
To check your SMTP server settings
1. Open Mach5 Mailer 4.5 and select the 'Mail'->'Program Options' menu. Click the "Server Settings' button located on the 'Send Options' tab. Be sure that "Use SMTP server" is selected, and enter the address of your mail server in the box.
2. If your mail server requires authentication, check the 'Use Authentication' box and enter your username and password in the appropriate boxes. Click 'Test Connection'.
3. If Mailer is unable to connect, it will ask you if it should 'Try to detect the SMTP settings automatically'. Click 'Yes'.
4. If Mailer is still failing, make sure your username and password are typed correctly. Most usernames are your full email address such as ''. Occasionally they are only the prefix such as 'username'.
The second most common cause of this type of error is a software Firewall installed on the PC which is silently blocking the application when it tries to connect to the internet. McAfee, Norton, Zone Alarm, and Kerio firewalls are all occasionally guilty of this behavior. Try temporarily disabling your firewall. This can usually be done by right or left clicking on the firewall's icon in your System Tray(where the clock is) and disabling the Firewall or exiting the application. Rebooting will re-enable the software if you exit the application.

Once you have changed your SMTP settings or disabled your software Firewall, you can send a quick test message.
1. Within Mach5 Mailer, the 'Preview' window ('Preview' tab located along the bottom of the Mailer window) has a button titled 'Send this Message'.
2. Clicking this button will ask you for an email address to send the mailng to. This is the easiest way to send a test email to various accounts.

Microsoft's Outlook Help also has a great article explaining why Relaying errors are more common in the age of SPAM.

A final possibility is a message limit per day, hour, etc imposed by your ISP or WebHost.   If you have hit this limit, your SMTP server may simply reject your connection with an 'Error 554 - Transaction Failed or Error 421 - Service Unavailable' message.

  Mailer includes the ability to limit its sending rate to stay within your ISP's email sending limits, and prevent your mailings from failing with the above errors.
 Drip Delivery Speed, Throughput Throttling, & Message Rate Limiting KnowledgeBase article.

For a complete list of SMTP error codes, has a great article:
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11-03-2017, 04:49 PM
Post: #2
RE: Failed Connection, Relay, and Socket Errors - SMTP Server Settings
thanks for the list guys. it'll really help me.
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02-12-2018, 05:20 AM
Post: #3
RE: Failed Connection, Relay, and Socket Errors - SMTP Server Settings
Excellent post. Thank you very much!!
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