Introduction
In order for Gravity SMTP to send messages from your Mailgun account, you will need to provide the plugin with a Mailgun API key. You must complete this step before configuring the Mailgun Integration within Gravity SMTP. This article outlines steps for generating a new API key in your Mailgun account. Reference Where Can I Find My API Key and SMTP Credentials? from Mailgun’s official documentation for more info and related articles.
Please note that Gravity SMTP does not currently support domain-specific sending keys.
Generating a New API Key
From within your Mailgun account, you can generate a Mailgun API key at Account → Send → Domain Settings → Sending Keys.
Note: Adding a sending domain to your Mailgun account is required to create a Sending Key.

You will then generate a new API key for Gravity SMTP to use. Click Add sending key, enter a Description for the new API key, and then click Create Key.

Your new key will be displayed only once. Be sure to copy and save this key as it will be used to connect the Gravity SMTP plugin with your Mailgun account. A single key can be used across multiple websites. However, if you ever need to revoke keys on a site-by-site basis, you may prefer to create one key per site.

Once you have added and verified a domain, you are now ready to configure your Mailgun Integration settings in Gravity SMTP.

IP Access Management
For improved security, Mailgun provides IP Access Management. If you find that messages are not being sent, please check that your site’s IP address is on the list of allowed IPs. When utilizing the IP allowlist, only the IPs you have specified will be able to connect to the API.