Troubleshooting Microsoft Office 365 SMTP server configuration
I’ve scoured the community forums for the most common Microsoft Office 365 errors so you don’t have to, and here are some of the most common ones:
- System.Net.Sockets.SocketException (0x80004005)
This error message means that you either don’t meet SMTP AUTH requirements or your network firewall or Internet Service Provider (IDP) are blocking ports 587 or 25.
In case you meet the requirements, here’s how you can check if you’re potentially getting blocked:
- Open Command Prompt (CMD) as an administrator
- Type ‘telnet’ to run telnet
- Run the following command:
open smtp.office365.com 587(25)
If you’re able to successfully connect, you will receive a response line similar to:
- 220 BY1PR10CA0041.outlook.office365.com Microsoft ESMTP MAIL Service ready at Mon, 1 Jun 2024 12:00:00 +0000
In case you can’t connect, try disabling your firewall or contacting your ISP.
- “SMTP send error. The operation has timed out”
Although a common error, this error is likely caused either by your antivirus software or firewall blocking your SMTP connection or a typo in your Office 365 settings. If neither of these solutions works, then the issue is probably on Microsoft’s end, in which case you’ll need to contact their support.
- 5.7.60 SMTP; Client does not have permissions to send as this sender.
If you’re seeing this error, check whether your application or email client is trying to send emails from a different address than the one you’ve entered in your SMTP configuration. The two need to be the same for the sending to work.
But, you can also give the ‘Send As’ permission to another address if you plan to use two different addresses for email sending.
- Transport Layer Security (TLS) encryption related errors
Recently, Microsoft has started rejecting connections to smtp.office365.com that use TLS1.0/1.1 for SMTP AUTH. So, make sure your device supports TLS version 1.2 or above.
But, if you need to use older versions of TLS for legacy clients and devices, you can:
- Go to Settings in your Exchange admin center
- Navigate to Mail Flow (under Security)
- Check “Turn on use of legacy TLS clients)
- Click “Save”
For more information on Office 365 and TLS, read the official Microsoft’s article.
Office 365 SMTP limitations or when not to use Microsoft Office as an SMTP server
While Office 365 does offer a reliable SMTP server, it has some considerable limitations that you should go over before deciding on it as your go-to option.
Namely, they include:
- Monthly subscription fees – To have access to Office 365 SMTP server, you’ll need to pay a monthly subscription. It has several pricing plans, with the basic one starting at $6.99 per month and allowing you to send emails to up to 10,000 recipients per day.
- It’s important to note that 10,000 recipients per day is not the same as sending 10,000 emails per day.
- No support for bulk email sending – Office 365 SMTP is not the most ideal option for sending large amounts of emails as the sending limit is the same for all pricing tiers. This means that even if you pay for Enterprise E3/E5 (the most expensive plan), you will still be limited to 10,000 recipients per day and 30 messages per minute, which can be a considerable issue.
- Lack of monitoring features – Typically, most SMTP service providers offer in-depth analytics and reporting features, which can help you optimize your campaign and improve your email deliverability. Unfortunately, this isn’t the case with Office 365.
- Steep learning curve – Getting the hang of Office 365 can be quite a challenge as it’s not the most user-friendly SMTP service out there. Add to this the wide range of features and services offered by the whole suite, and you’ll realize why most new users may even need training to navigate Office 365 complexities.
Consider an alternative — using Mailtrap Email Sending
If you’re like me and Office 365 SMTP limitations are too much for you, don’t worry—I have just the right solution.
I use Mailtrap, an Email Delivery Platform for developer teams to test, send, and control their email infrastructure in one place.
Personally, I needed to send bulk mail, so I used Mailtrap’s Bulk Stream to send large amounts of marketing and promotional emails in my high-volume campaigns to enhance my deliverability even further.