What Are Mailbox Providers?

In This Article:

Mailbox Providers are services that handle the receiving and sending of emails by the end-users. These include free tools and corporate solutions such as: 

  • Gmail
  • Google Workplace
  • Amazon SES
  • Cisco Email Protection
  • Mimecast Email Protection
  • Microsoft Outlook
  • Yahoo

Under the Mailbox Providers tab in Mailtrap, you can see detailed stats for each mailbox provider of your recipients.

With this information, you’ll know which mailbox providers your recipients use and which are the most popular. This will help to better understand your audience and adjust your emails to properly display at mailbox providers the audience prefers.

Tracking the performance of each email provider is important to ensure high open rates and prevent bounces and spam. Plus, it helps you to improve your domain reputation.

The following sections detail how to take advantage of Mailbox Providers feature within Mailtrap Email Sending.

How do we know the recipient’s mailbox provider?

We don’t actually know the recipient’s mailbox provider until the delivery attempt. And this is what happens when you send emails via Mailtrap servers. 

  • Mailtrap makes a delivery attempt. 
  • Mailtrap receives the response from the mailbox provider (successful or not).
  • When Mailtrap gets the response, we know which mailbox provider it is.

Click on Mailtrap Email Logs to see mailbox provider MX record. You can find the mailbox provider MX record by clicking on an email under Email Logs, then selecting the Event History tab. 

Note: Recipient and sending IPs have been removed from the image for security

Why is it important to monitor mailbox provider stats?

It’s important because the deliverability towards a specific provider can suddenly drop. This is a clear sign that a provider has started treating you negatively, so it’s critical to take action to improve the situation. 

As there are different reasons for subpar deliverability, it might be tricky to determine why the deliverability drops. For example, mailbox providers can change their server policies. Or, your emails’ new content can trigger one or more of the given policies. 

Note that mailbox providers don’t publish their anti-spam and security policies, but that’s okay. If they did, spammers would abuse the information. 

Also, spam check is built into Mailtrap. Moreover, the SpamAssassin that we use is also widely used by mailbox providers to determine whether an email should go into spam or not.

To learn more about the SpamAssassin, click here.  

Mailbox providers filters 

Mailbox Providers Overview panel allows you to filter by Domains, Mailbox Providers, and Categories. Here’s how to use each filter. 


  1. Click on arrows in the All Domains box. 
  2. Choose one or more domains you’d like to use. 
  3. When you select the domain, the Table automatically shows corresponding statistics.

Domains are all the Mailtrap-verified websites you use for sending. The drop-down list includes both active and deleted domains. We keep the deleted domains to preserve the historical data so you can further improve your sending.

This filtering is also helpful when you send from multiple domains and want to check the mailbox provider stats of emails sent from a certain domain. For example, this helps ensure the domain reputation doesn’t worsen when you send to a particular provider.

Tip: You can click “Clear Filters” to automatically reset the filters to default values. 

Mailbox providers filter

  1. Click the arrows in the Mailbox Provider box.  
  2. Choose the provider you’d like to use. 
  3. Check the corresponding stats in the table below.

As already mentioned, Mailbox Providers are services your recipients are using to send and receive emails.

You can select a few providers at the same time - just repeat the actions listed above. If you want to remove a provider from the filter, click X next to the provider name.

This filter is helpful when you want to compare stats across multiple providers. When you select the desired providers, there’s no need to scan the whole table. 


  1. Click the arrows in the Categories box. 
  2. Choose a category or categories. 
  3. Preview the stats for that category in the table below. 

Email categories are different types of transactional or marketing emails sent to recipients. These can be welcome emails, change password emails, critical update emails, etc.

Plus, this filtering is helpful to see how different email types are treated by different mailbox providers. For instance, you might see that your new promotional emails have worse Open Rates compared to the previous batch. Or, you might see that the Open Rate for your Invoice emails significantly dropped only at Gmail.

With Mailtrap, you need to set up the categories yourself, which allows you to have a more custom categorization. That’s important because it gives you a clear idea of which type of email performs well.

To set categories, you need to insert the category name into the “X-MT-Category” header. For example, let’s see what that looks like if you’re using cURL during domain verification.

curl --location --request POST \'https://send.api.mailtrap.io/api/v1/sg_send' \--header 'Authorization: Basic YXBpOjgxGDYxYjg4ZTSlSGQ2MjQyNTFhMzk1MmNhY2N3ZTJh' \--header 'Content-Type: application/json' \--data-raw '{"personalizations":[{"from":{"email":"from@test.com","name":"From Name"},"to":[{"email":"your_email@example.com"}],"subject":"You are awesome!"}],"headers":{"X-MT-Category":"Test Order Confirmation"},"content":[{"type":"text/plain","value":"Congrats for sending test email with Mailtrap!"}]}'

The title (Test Order Confirmation) in the X-MT-Category header shows which type of email you’re sending. 

Filtering by date

Mailtrap allows you to filter by specific dates for an unlimited period. To filter by date and change the reporting period, click on the upper right corner of the screen.

Select the period you want to preview and hit Apply. By default, Mailtrap provides the data for last week, including today.

The Mailbox Providers Overview window populates Table, Charts, and Timeline tabs based on the selected filters. These are helpful to understand the emails’ performance, so it pays to take a closer look at the information featured in each tab. 


The first column features Mailbox Providers of your recipients.

Note: If no emails were sent from a given domain, the table will show that there’s No Data. The table provides comprehensive data across all active domains for the time period you selected. 

The stats include the number of Delivered emails. You can also see Unique Opens and Unique Open Rate, as well as Clicked emails and Click Rate

Also, the Tables tab shows Bounce emails and Bounce Rate, plus Spam and Spam Complaints. Finally, you can see the Clicked to Open Rate

The given stats are important because they tell you about email performance with different providers. The numbers help you understand how email providers perform against each other. Or if you need to worry because of increased spam complaints with a particular provider, for example. 

You can learn more about Stats here.

Color coding

To immediately understand email deliverability, the table features colors that signal if the value is good, bad, or just average. 

We use straightforward green, yellow, and red colors to differentiate the satisfactory results from the ones that need your attention. 

For example, you might see that the Unique Open Rate is green with one email provider but red or yellow with other providers. That may indicate that you need to make certain tweaks in the email to boost the rate. Or the emails aren’t actually reaching the recipients’ inbox for a particular provider.  

If you want to know more about the differences in color coding, check out this article. Note that we’re only color-coding certain stats, not all of them. And here are quick explanations on how to interpret the colors:

  • Green - good results - exceed what we perceive as a satisfactory value for a particular data point.

  • Yellow - borderline results - neither good nor bad, and may require your attention or action. If the Unique Open Rate is <95% of the average Unique Open Rate for the selected filters and period, we label the stats yellow. With Bounce Rates, the warning level is between 2%-5%. And it’s between 0.08%-0.1% for Spam Rate

  • Red - the result is under the threshold we consider satisfactory and it requires your action to improve the performance of a specific mailbox provider. If the Unique Open Rate is <80% of the average Unique Open Rate for the selected filters and period, Mailtrap labels the stats red. The Bounce Rate warning starts at 5% and the same goes for Spam Rate higher than 0.1%.  

To stress, Mailtrap provides the average Unique Open Rate for your account and the filters selected for a particular period.

Check out our Stats article to learn more about how we define the threshold values.

Note: The results for all stats above the warning level thresholds are labeled green. Also, the threshold levels are based on cross-industry research and we’ll give you the option to set your own in the future. That doesn’t apply to Unique Open Rates which are based on your average. And, for now, you can just toggle off the color coding by clicking on the associated button. 

What happens if you click on a mailbox provider in the table?

You’re taken to Email Logs where you can preview all sent emails meeting the selected criteria for a particular provider. Plus, you can use a combination of many filters for more specific search results. 

For example, the first filter allows you to choose a specific recipient, email subject, number of clicks or opens, etc. When you click on the second filter, you can choose " If" or "If Not". “If” filters the delivered emails and “If Not” shows the ones that haven’t been delivered. Also, the last filter shows which email provider you selected; Google, Yahoo, etc.  

Then, you can click on individual emails to get more detailed information for each one. 

This option is beneficial because you get quick access to specific emails and all logged data. So, it should be easier for you to spot errors and find points for improvement. 

To find out more about Email Logs, click here


The Charts tab takes key metrics for the selected period and displays them in box graphs. You get an overview of Unique Open Rate, Click Rate, Bounce Rate, and Spam Complaints

The x-axis (horizontal) represents the selected time period and displays values recorded each day. The y-axis (vertical) is a visual representation of the respective rates for a given day. 

Dragging your cursor along the chart line reveals the percentage points on each day for the selected time period. 

The peaks show the activity increases on a particular date, compared to the previous date, and the same goes for the lows. 

It’s possible to see 200%, 300%, or even higher increases from one day to another. This is fairly common because the recipients might not open your emails on the delivery date. Or they might not click on the links the same day. The same thing happens if there are more opened than sent emails on a certain day. 

Note that these data points are color-coded. Green signals a great percentage, yellow signals something to keep under your radar, and red signals the results you want to improve.

Also, the color coding relates to the filters and time period you previously selected. But you can play with filters and the mailbox provider, domain, or category to narrow down the Charts overview. 

Lastly, the Chart tab helps you to get more accurate insights into recipient activity on each day for the selected time period. Basically, you get a quick overview of the emailing dynamics. 

The benefit of this is that you can clearly understand when a certain change occurred - e.g. in case of a sudden drop in one of the metrics.

Note: You want to keep Bounce Rate and Spam Complaints low. As mentioned, the threshold for Spam Complaints is 0.10% of the emails delivered. So, low values within these graphs are favorable. 

Tip: If a certain variable amounts to zero, you’ll see an empty coordinate plane. Typically, that occurs if no events happened, for instance, no Spam Complaints or no opened emails on that day.

Using email log feature

You can quick-access the Email Log by clicking on the corresponding label under each chart. The action reveals a list of emails for each sent email filtered based on the chart category you selected.  

For example, if you click Email Logs under Unique Open Rate, it will show all open emails for the selected reporting period. 

Note: Email details have been removed from the image for security.

The Email Log under Click Rate reveals all emails that received at least one click. And clicking the same label under Bounce Rate and Spam Complaints shows which emails bounced or got labeled as spam.


The Timeline tab is very similar to the Table tab - it displays the same data. But, it drills down to the stats for each day based on the time period you selected.  

This tab is particularly useful when you send a lot of emails and want to compare the daily statistics. With that, you can easily see when your recipients are most active. Or if there are days with very low activity despite the high number of delivered emails. 

As a result, you’ll be able to improve sending schedules and potentially spot trends in the recipients’ behavior.    

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