It is useful to know if the e-mails you send to your customers, lead and suppliers have arrived at their destination and if they have been read.
Indeed, your e-mail address may be seen as a SPAM address.
Therefore, it is useful to transit through a paid email routing service.
In other words: instead of using the classic SMTP server (= email server) of your email address,
you're going to go through an email routing company. The two world leaders are SendGrid and MailJet.
The two links provided allow you to register. MailJet provides a free offer with 6000 emails sent per month and SendGrid a free offer with 2000 emails per month.
Then it's up to you, if necessary for the paid version that suits you best.
Finally, Simple CRM allows you to directly view desirability reports from these two professional SMTP providers.