Best practice

Subject lines should be under 60 characters (unless absolutely necessary), using simple English, and prepare the reader for what’ll be inside.
Subject lines with questions or personalised fields tend to work best.
Clean data is incredibly important - your deliverability and the effect you can have on new/prospective data will depend on it.
Clean data (yep, we're saying this one again) in Hubspot is key. We have a lot of properties within the business, and they need to be kept up-to-date.
Triggers should be fully tested and QA'd before automations are set live.
Communication amongst teams will be integral. If there's someone we shouldn't be speaking to, let us know!

Tone of voice should remain consistent and friendly/positive.
Proofing - mistakes sometimes happen, but we should be proofing every email to minimise the likelihood of this happening.
Be concise, don't use 50 words when 20 will do.
The role of email is to get them through to further information - don’t overfill.
Don’t use first name personalization too often, it becomes disingenuous.
Relevant, tailored emails work best.
Make sure everything sticks to the purpose of the email.

Limit the use of Images with words on - it's not best practice for accessibility.
All images should have adequate alt text.
The first CTA of an email should be above the 600px “fold” (or as close to it as possible).
Real estate is precious, use it. CTAs in the top right-hand corner of an email, when relevant, can be gold dust!
White/blank space is your friend, it makes things easier to read.
Consider using design principles like the Z-pattern; these work in email like they would elsewhere.

All emails should have the ability to be viewed online.
All emails should include relevant T&Cs, privacy policies and unsubscribe/preference options.
A/B testing should be conducted often, if not always.
CTAs needn’t always be physical buttons - using underlined/bolded words with arrows works very well too.

How many emails are sent a day, globally?