Sending a test SMTP email with Telnet is one of the most basic tests you can do. This test is useful in checking the connection and determining if the most basic of problems:
Is the server up?
Is there a firewall blocking communication?
Does the mail server allow for relaying of a particular domain/email address?
What SMTP commands does the mail server support?
Does the server respond with the correct hostname?
Does the connection work outside any third party software or APIs?
The <%subject%> property is used for both Text and HTML templates.
The text property is substituted into the <%body%> of the text template and html is substituted into the <%body%> of the HTML template.
Text or HTML Templates?
(information)
Info
It is best practice to provide content for both the html and the text properties in all of your emails.
If the text property is present, but not html, then the resulting email will only contain the text version of the template, not the HTML version.
Enabling a legacy template means that the subject and body
content of your message will behave differently.
If you want only the message's content to be displayed, populate only the token in the template's field.
If you want only the template's content to be displayed, leave the message field (subject or body) empty, and the template will populate.
Advanced options
You can use X-SMTPAPI substitution and section tags in your template's subject and body content, and they will be replaced with the values specified when you send the message.
Substitution Tags
Substitution tags allow you to generate dynamic content for each recipient on your list. When you send to a list of recipients over SMTP API, you can specify substitution tags specific to each recipient.
Section Tags
Section tags allow you to substitute in content in an SMTP message. Section tags are similar to substitution tags but are specific to the message, and not the recipient. Section tags have to be contained within a Substitution tag since SendGrid needs to know which data to populate for the recipient.