Just want to point out that if the only emails your server sends are CiviCRM emails, then if the provider offers SMTP relay then you don't even have to install an extension. For example Sparkpost (not advocating for them over others, just as an example, although I am leaning towards them) has this page for instructions:
If your server does send out other emails then if you're handy with mail server config you could probably adjust the above to only relay for the emails that are coming from CiviCRM.
However in this case you should check for bounces using the "bounce processor" in CiviCRM. The main advantage of webhooks is that they avoid having to setup a mailbox for this. Another advantage of webhooks is for managing spam complaints.
It may sound silly, but someone might fill in a form on your website, do a typo in their gmail/yahoo email address, someone else receives it and clicks the "this is spam" button on their webmail. Another useful use-case is for managing bounces from contribution receipts (by default CiviCRM does not have a way to detect those boucnes).
I have been using Mailgun. We send 300,000-ish emails per month. I update the Mailgun webhook extension and currently use it on 4.7. https://github.com/blackbricksoftware/uk.teamsinger.civicrm.mailgun
We currently use Amazon SES (SMTP) to send out emails from CiviCRM from multiple digitally signed & verified domains.
We also use Amazon SNS to collect all bounces/complaints and send them all to one email address to be processed by CiviCRM
We only needed to make a very minor change to CiviCRM's mail processing to read the SNS formatted VERP bounce backs.
This combination is very cheap (25$ per month to send ~180'000 emails) and really simple to maintain once setup. Anyone on the system can send out emails and receive replies using any of the verified domains but all bounces/unsubscribe can be handled in one mailbox.
Just want to emphasize that the Sendgrid CiviCRM extension is not compatible with WordPress, although it is listed as CMS independent. https://civicrm.org/extensions/sendgrid-event-notification-processor
But Andrew provides a pull request for a fork that is compatible with WordPress here: https://github.com/imba-us/com.imba.sendgrid/pull/1