How to properly organize E-mail messages for users?

Question

Email

Maybe someone will advise where you can get information, or share experience.
I plan to launch a 2B2 resource. To start the project, for a long time I have been collecting e-mails of companies for whom the site will be oriented. As a result, I have collected 20 yew. e-mails of companies and I need to use them as efficiently as possible to start the project, with the highest efficiency.
How to organize this in order to deliver as many letters as possible, and then work with users in a segmented way: organize a series of letters on working with the site for registrants, and continue to invite the rest to the site so as not to strain anyone with unnecessary letters, but periodically remind about the project.
I would like to use services like https://sendgrid.com/smartresponder.ru
According to what scheme can they be integrated and work with them? Are there examples somewhere?
How to take into account those who have registered and should already receive other letters. Do I need to keep track of registrations and manually change the subscriber group or is there an API that will allow this to be integrated?
The site will also send standard e-mails for the business portal (about messages received by the user, new offers, reminders, etc.).
I would also like to send these letters through mailing services, since they can be analyzed and not fall into spam. Is this my unhealthy idea, or do they also do such integration? Now I have a portal where I send everything myself from the site, but, in my opinion, this is yesterday, I don’t feel the audience, and maybe part of the work on the new portal can be transferred to the mailing service.
That's how to make the most of my precious 20 tis. e-mails and establish further contact?

Answer 1

mailgun.com