Not all email clients are formatting the `ping.body` contents uniformly. Even using different applications from the same email provider results in a different display of the `ping.body` contents. There are two basic issues:
* Not all email clients are honoring the fixed-width font that should be used inside `<pre>` tags. Using fixed-width font is listed in the definition on https://www.w3schools.com/tags/tag_pre.asp
* Not all email clients are displaying the text with a 1em line height. This was a recent change to the healthchecks WebUI in 9fd9c8e4ef but is not part of the definition of the `<pre>` tag. I'd like to add this to the emails to make Healthchecks more uniform between the website and the email notification.
Gmail Webmail:
- [x] Is using fixed-width font
- [ ] Line height is set by the webmail client to 18px
Gmail Android App:
- [ ] Text is not fixed-width
- [ ] Line height has extra padding
ProtonMail Webmail:
- [x] Is using fixed-width font
- [x] Line height is correct
ProtonMail Android:
- [ ] Text is not fixed width
- [ ] Line height has extra padding
The testing I performed is not extensive, but it does show how multiple clients are displaying the contents differently. To make the display of the `ping.body` more uniform I'd like to add a bit of formatting information to the `<pre>` tag.
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