Template & Client Compatibility

[dm17]

I'm trying to find information on what makes Mosaico or MailChimp "more compatible with more email clients" - as I've seen many claims on this topic.

1. How do we know that the many email clients in the wild will display our mosaico/versafix-composed email as accurately as they display MailChimp-composed emails?

2. How can such a thing be known besides the amount of testing MailChimp must have done, considering its popularity?

3. What makes a template compatible with an SMTP relay? For example, if we compose with Mosaico and then send with Sparkpost or Sendgrid...

4. Are MailChimp and Mosaico templates cross compatible?

5. Considering the reporting features on Mosaico: how do the developers consider optimal integration with an SMTP relay, which does its own analytics and reporting?

Apologies, but this area is a bit opaque to me - and it seems this is true for many because of the lack of details in articles about newsletter compositing, WYSIWYG editors, and "compatible templates."

[bago]

A) Mosaico is template based, so compatibility depends on the template being used.
B) It is really unfair to think that Mailchimp compatibility is better just because they are big: just look in the internet to see WHO publish reports about email client issues and you won't see Mailchimp, there, but minor developers. E.g. the infamous 1px pixel bug from Outlook have been first reported by ME, even if it appeared for every sender, including Mailchimp ( https://mosaico.io/email-client-tricks/outlook-2016-weird-1px-horizontal-lines/ ). The most compatible technique to date, aka Fab4 ( https://mosaico.io/email-client-tricks/fab4-responsive-beyond-gmail/ ), have been shown by Rémi Parmentier aka HTeuMeuLeu, the author of "caniemail" ( https://www.caniemail.com/ ): no big email marketing service names like Mailchimp behind those stuff, because real innovation/evolution happens elsewhere.
C) I'd bet versafix-1, our master template, to show better compatibility than anything you will find around: of course everyone is good at most common clients, but you should check edge use cases, like gmail webmail from a smartphone (not the gmail app, but the gmail webapp through the mobile browser), or gmail app reading a non gmail email via IMAP (GANGA).

To answer your question:

1. I'd bet mosaico's "versafix-1" is more accurate (more compatible): do your own testing and report issues to the versafix-1 repo, if you find mailchimp is better: the more edge cases (e.g: country specific webmails/app) you'll test the more it will be clear.
2. wrong assumption.
3. this is a matter of what smtp relay service do: they should not break html, but if they do it is an issue in their service: we don't care of them: it is already a PITA to care of most email clients. If your smtp relay service changes your html when sending, simply switch to another service.
4. I don't know what you mean by this question.
5. "reporting features"? Which reporting features? Mosaico is just an email composer.