Realtime bounce reporting

[jace]

One of the most common support request categories with Hasjob is for bounced email. We currently resolve this by looking up Sendgrid's logs. However, since Sendgrid provides an API, we can:

1. Periodically use the API to look for new bounces (where "periodic" can be 1-5 minutes after any verification email is sent)
2. If a bounce is detected, post a notice to the user(s) who attempted using that address, and
3. Show this notice to the user the next time they are on the site, and possibly tag the related JobPost as well. To make this work we'll need a messaging layer in Hasjob (possibly replacing JobApplication as well).

In addition, since valid addresses sometimes bounce because their mail server doesn't like our mail server, tracking these mail servers can help warn the user of a possible bounce. Example from a bounce today:

$ host -t mx zotlay.com
zotlay.com mail is handled by 20 mx2.zohomail.com.
zotlay.com mail is handled by 10 mx.zohomail.com.

While it's not possible to determine the reason for a bounce without having a human examine the bounce message, we can (a) maintain a list of MX servers that tend to bounce, (b) cross-check all email addresses for matching MX servers, and (c) alert the user.

[jace]

Sendgrid bounces API. https://sendgrid.com/docs/API_Reference/Web_API/bounces.html

[jace]

The messaging layer described above now has a separate ticket in #352.

[pranshu-07]

@jace maintain a list of MX servers that tend to bounce -> Will give you false results for some valid email address which tend to deliver. Email bouncing not only depends on MX servers relation with your mail server. There are pretty much other factors related to it.

Bounces are generally categorized in 2 - soft-bounce and hard-bounce. In case of soft-bounce, Sendgrid would likely to retry on his end.

I suggest you to just alert users after their address bounced by any reason (if possible).

[jace]

While it's not possible to determine the reason for a bounce without having a human examine the bounce message, we can (a) maintain a list of MX servers that tend to bounce, (b) cross-check all email addresses for matching MX servers, and (c) alert the user.

MX Sniff is a new project to identify MX providers given a domain or email address, to help implement this feature.