Is Microsoft Graph API using SMTP at the back?

I am trying to use Graph API to send 20 messages within 1 minute to certain teams channel. Does Graph API use SMTP protocol to send email?

POST /me/messages/{id}/forward
POST /users/{id | userPrincipalName}/messages/{id}/forward
POST /me/mailFolders/{id}/messages/{id}/forward
POST /users/{id | userPrincipalName}/mailFolders/{id}/messages/{id}/forward

Is Microsoft Graph API using SMTP at the back?