So far I'm only seeing it on PC webmail.

It’s on tablet too. Using app on iPad. Don’t know on phone, I’m not using beta on it.

I get the sidebar calendar on iPad Pro Safari webmail and the Fastmail app,
and on iMac Safari webmail

Found it! THANKS!

/cl

I'm using a PC, Windows, with Chrome Browser.

Contextual sidebar and improved contacts
 

Contextual sidebar
Access your calendar while reading a conversation, or quickly find the contact info and related messages for a participant in the thread.
See all attachments in the thread grouped together.

Improved contacts
Easily take actions with the information you have stored for a contact.
See messages and events they are involved in. Quickly find your recent contacts.

@Fastmail on Twitter:

This is an awesome feature. Just last week, I was going through contacts and thinking, I don't know who these people are, and whether I should save them or not.

NOW?!?!?

I can click on a contact and instantly see the email communication I've had with them.

EXCELLENT!!!

Now, please, more ways to import Contact photos from gmail / other sites? :)

Thanks fastmail, new contacts are AWESOME!

Withdrawn from beta at the moment.

That's interesting; I still have it.

Checked. It seems it has disappeared from the mobile interface (iPad). It’s still there on the desktop interface.

Fastmail v3.3.0 for iOS/iPadOS and current contextual window
 

The iPhone iOS and iPadOS Fastmail apps are available, and I updated both within the past few days (April 21 and 24). The new version is 3.3.0, and when you first enable beta you are notified as follows:
At this time, the iOS and iPadOS interface are very similar to each other (except for the screen space). But they differ from the web interface. Here is what I see with a threaded interface active:

• Web beta interface: An icon in the upper right corner of the screen (to the right of the More button at the top) toggles the right sidebar on and off. When viewed, the right sidebar has three tabs:
  • Calendar: Shows your calendar. This is not context-related to the message your viewing, and is simply your current normal calendar.
  • People: If a message is selected, this shows the senders and "other recipients" in the thread.
    • If only you (at your default address) and one other person are in that thread, you will see that person's contact details, a list of recent mail messages to/from that person (and a link to search for all such messages), and the calendar events with meeting requests using that person's email address.
    • If more than one person is in that thread, you will see a circular icon (to the left of the sender name) with the name or image associated with that contact. Click the circular icon or image to see the information for that person.
  • Attachments: Shows all attachments in the thread, including the contact who sent the message with the attachment and the date of the message.You can immediately open the attachment (for example, in Word) or download it to your PC.
• iOS and iPadOS beta interface: There is no longer an icon in the upper right. Instead you simply select the circular icon (as described above) to the left of the sender name. You may need to select it twice, one time to view that one message and a second time to bring up the new contextual information.
  • On an iPad, instead of a sidebar there is a pop-up window.
  • On an iPhone, instead of a sidebar (which would be difficult due to the small screen size), the contextual information about that contact is shown full-screen.
  • On both the iPad and iPhone, at this time only the People contextual information is shown - see above for details. There is no contextual calendar or attachments information.
• On all devices, the People contextual screen includes buttons near the top to call, send a text message, compose an email message, or send a calendar invitation to that person.

My guess is that Fastmail will add the calendar and attachments feature back to the iPadOS and iOS versions. Just remember that you need to select the new icon (containing either the initials of the contact or their picture) instead of the upper right contextual icon.

A new feature in version 3.3.0 and the web interface is ability to sign up for a Fastmail account from the login screen of either the mobile or web interface. On the web interface the Sign Up button is in the upper right corner of the screen.

Bill

This feature seems now to be generally available, I have it now. I can echo this sentiment; getting the context of past conversations is incredibly useful. I have a SIP phone on my computer, so clicking contacts' phone number and just calling through is additionally great.

I also like the execution.

Just one improvement would be to have the "people" tab the default tab / first tab in the panel (although it remembers the last selected panel, so no issue there).