SMTP Relays for Email

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This article was written to define Simple Mail Transfer Protocol (SMTP) relays, and the use of SMTP in your e-marketing efforts within the CRM. This article is divided into the following topics:

SMTP Relay

Below you will find some information on the SMTP relay providers we recommend. You are not limited to the providers listed in this article. These are just some recommendations that we have researched for you.

Important: Centrex does not support SMTP with O365 any longer. We sent out a deprecation notice about this in Aug/Sept 2022.  Clients must use another provider for sending emails.

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What is an SMTP Relay?

SMTP relay refers to the type of SMTP that can be authenticated using a username, password, and host URL. This is the type of SMTP service that will work with our E-Marketing senders. You can find some more information on setting up senders in our article on setting up an E-Marketing campaign.

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How many emails do I send?

You have the capability to export your record of "Past Sent Campaigns". Click on the E-Marketing tab, and then click on the "View All Sent" button on the left side of the page (see first image below). E-Marketing_View_all_Sent.png

After clicking on "View All Sent", you will see a table of all past sent e-marketing campaigns. By clicking on "Export to CSV" (see image below), you will download a .CSV file to your Downloads folder. From that .CSV file, you should be able to determine how many emails you send using your spreadsheet software (Microsoft Excel, Google Sheets, etc.) to help you determine the size of the plan you will need.

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Can I use my personal email's SMTP settings?

No, you want an SMTP relay service meant for sending large volumes of emails. Your personal email's SMTP will likely have a sending limit that will stop messages from being delivered and cause your domain to be flagged as sending spam. It is not meant for email marketing. You will need to enter the SMTP credentials for your user under the My Settings page so that individual messages sent by you will go out through your server.

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How to enable SMTP Settings for Clients

Regardless of who is your outgoing SMTP (simple mail transfer protocol) provider, you may be required to complete a few steps to ensure the functionality operates properly with our CRM.


Some security protocols include a 2-Step Authentication (2FA) when logging into a new device, product, or location, even when 2FA is not enabled. An error message like the one below may result if more configuration is required. 


This is for use on individual user profiles.

NOTE: We recommend that you not use Google SMTP for senders to be used in e-marketing campaigns.


Troubleshooting Bad Credentials

If you received an error message like the example shown above after entering your credentials for outgoing mail settings and clicking Test SMTP Settings (see image below), the SMTP Provider may be preventing authentication as part of their security protocols. 


To fix this, you will need to activate 2FA and use an APP Password. This message can also be found in your system logs. 

If your SMTP credentials have been successfully authenticated you will see the message below. 


STEP 1: The first and most important step to troubleshoot your credentials is to double-check your username and password have been entered correctly. The following steps may require you to make changes to your SMTP Provider configuration that will not work if your username and password are incorrect. 

STEP 2: We recommend activating and using 2-step Verification even if you are not having issues with your SMTP. This is quickly being adopted and enforced on many platforms. For an example of more information regarding 2-step authentication, visit Google 2-Step Verification.

STEP 3: Generate an App Password, which is a multi-digit passcode that gives a less secure app or device permission to access your Account. App Passwords can only be used with accounts that have 2-Step Verification turned on. Basically, this acts similarly to how an API Key works. It is a dedicated password to be used in an outside system. If you are using 2FA with your SMTP Provider, you may need to use an App Password in your outgoing mail server settings. For information on generating an APP Password in Google, visit Sign in using app passwords.


Additional Information / Sources


Mailjet is a good offering for clients with low to moderate E-Marketing volume. It has accessible features that aren't too advanced for anyone who isn't an expert in email marketing but enough that you should find it adaptable as you grow.



Free up to 6,000 a month (200 messages a day). Beyond that, they have plans starting as low as $13.50 per month (15,000 emails/month). You can find more details here.



Mailjet provides a large number of resources you can access to prevent your SMTP from getting blocked and also implement practices that will lead to successful campaigns. Below are some resources we recommend reading.

Compliance Guide - Guide on how to run campaigns within compliance of the law and system framework.

Authenticating Domains with SPF and DKIM - It is important you set up an SPF record for your DNS (Domain Name Servers), this helps prevent your emails from being identified as Spam.

Email Statuses - Explanation of the different statuses of messages going through your SMTP. The section about Bounced and Blocked message are particularly helpful. 

The Different Types of Emails - Explanation of the different types of emails you use in E-Marketing. Understanding the difference can help with the success of your campaigns. 


Setting up a Sender

You can find some general information about E-Marketing campaigns including setting up a sender here. You will need the SMTP settings from Mailjet to complete setting up a Sender. 

On the SMTP settings page (go to Account settings →  SMTP and SEND API settings), you will find your username and password (API Key & Secret Key), along with the Mailjet SMTP Server name, and ports.


Once you click on Retrieve your API credentials, it will take you to the API Key Management screen (see below). Under the Primary API Key section, the API Key Field will be used as the username, and the secret key will be used as the password.


We recommend using TLS on the Sender in Centrex. 

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SendGrid is the SMTP service used by Centrex for all of our transactional emails (email triggers, e-sign requests, etc.). It is good for organizations sending a large volume of emails and offers a lot of controls for managing your server's reputation. Most may find SendGrid too large a tool for their needs, but for those consistently sending a large volume of messages who want to have complete control of the SMTP server's reputation for their campaigns, this may be the best option for you.



SendGrid offers two (2) types of plans; one with a Shared IP and one with a dedicated IP. Having a dedicated IP might be necessary depending on the volume and types of emails you are sending. Using a dedicated IP lets you manage your server's reputation and will mean you are not subject to a shared IP's reputation. 

The Essentials plan offers up to 40,000 emails a month for $9.95 per month with pricing increasing every 10,000 emails per month. This plan does not include a dedicated IP.

The Pro plan offers 100,000 emails a month for $79.95 per month and includes a dedicated IP. 

The Premier plan requires custom pricing (contact SendGrid for more information) and 2,500,000 emails a month. This plan comes with a dedicated IP and prioritized support. This plan is likely too large for most clients.

You can find details about SendGrid's pricing here.



SendGrid does offer support documentation on their site as well as customized personal support with their upgraded plans. You can find all their support materials here.  


Setting up a Sender

Sendgrid requires you to create an API associated with the SMTP Relay and provides a random string you will use for the password. Once created, the username will be "apikey" and the password will be the string of characters provided by SendGrid. You can create an API Key once logged into the user dashboard under "Settings" along the left-hand side. Once entered, the SMTP Setting should look something like the image below.


You can find more instructions on setting up the API Key and using it for SMTP here.

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