Knowledge base

How to send emails via SMTP with MailerSend

What is SMTP?

SMTP or Simple Mail Transfer Protocol is the standard set of rules by which emails are sent, received and relayed over the internet. Regular email clients (Gmail, Yahoo, Outlook etc) all use SMTP to send your message to a mail server that then uses SMTP to relay that message to the correct recipient server.

How to send emails via SMTP

To send emails using SMTP:

1. Navigate to the Domains page.

2. Find the domain from which you want to send emails via SMTP and click Manage.

Domains page in MailerSend.
Note: Your domain must be verified in order to send emails.

3. Scroll down to SMTP and toggle the switch labeled Send emails using our SMTP servers instead of our REST API to enable SMTP.

Note: You will still be able to use the API if you enable SMTP.
SMTP toggle switch

By enabling SMTP, the following information will be automatically generated:

  • Server (SMTP host)

  • Port

  • Username

  • Password

SMTP toggle switch enabled

You will be required to enter this information into your content management system either directly or via a plugin. Either way, all systems will require you to enter your Server (SMTP host), Port, Username and Password.

Note: SMTP credentials are not exclusive to specific domains. All SMTP credentials can be used account-wide for any verified domains on the account.

How to troubleshoot SMTP emails not sending

Please note you won't be able to send any emails if:

  • Your account is unverified

  • You're sending from a different FROM email address than your verified domain

  • You've reached your account's quota

  • The reply-to email address is invalid

Additionally, you may be asked to provide the type of encryption. You must always use TLS encryption.

Note: If you’re using Wordpress, there are multiple simple plugins that can be used to enable sending emails via SMTP such as Easy WP SMTP.

What’s the difference between SMTP and API?

The key difference between SMTP and API is that the SMTP uses multiple back-and-forths between the client and the server to communicate whereas the more feature-rich API receives HTTP requests directly from your app and the email sending is triggered directly from there.

Additionally, without the help of an integration tool such as Zapier, some coding knowledge is required to send emails via API whereas no such knowledge is required to send emails via SMTP.

Now and again SMTP may be the only option available depending on your limitations. For example, perhaps your content management system only uses SMTP and you don't have a developer available to write the code required to switch to sending via API.

To determine which route is best for you, compare the two below.

SMTP Relay



SMTP (Simple Mail Transfer Protocol)

HTTPS (HyperText Transfer Protocol)


- Simple set up

- Requires no coding

- Easy to test

- Straightforward troubleshooting

- Optimized security

- Quick email deliverability

- Ideal for bulk sending

- Compatible with MailerSend templates


- Slower performance when sending in bulk

- Emails are not triggered automatically

- MailerSend templates can’t be sent via SMTP

- Requires some coding skills

Ultimately, the choice is yours. If you’re a casual email sender with a simple content management system, SMTP relay may be what works for you; whereas bulk senders and app developers may benefit more from the use of email API.

Need more info?

Feel free to reach out to A member of our support team will gladly assist you.

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