We are presently in the process of implementing Calendar support in Mailspring! The preview version has been available for some time, and we hope to have a full release version of the feature shipped soon, hopefully this year.
Original issue: Feature Request: Calendar Support · Issue #199 · Foundry376/Mailspring · GitHub
“Hopefully this year” sounds funny … maybe next year ? or the next one? Does not matter, calendar has not been implemented in the last 5 years 
@dido-b I say “hopefully” because there are a lot of major bugfixes and stability upgrades that have to be done this year, and that may potentially push back the Calendar. That’s been the case for some time; as you can imagine, the stability and usability of existing features is more important than adding new features. (There’s even another feature slated for this year that has been more in-demand than the Calendar, so that has to come first!)
Historically, Mailspring has just one developer (@bengotow), who works on this project in addition to a full-time job. Over the last couple of years especially, the sheer mass of the issue list on GitHub — much of which consists of questions, minor edge-case bugs, duplicate issues, and wishlist feature requests — has made it difficult to find and focus efforts on the most urgent bugs and features, especially given limited development time. Software development is time-intensive at best, and Mailspring is a particularly complicated project.
That’s why I was brought on as the Volunteer Community Manager. I can determine the most urgent bugs and highest demand features, with an eye towards the actual development effort involved.
All that to say, patience — yes, even years of it — is more than warranted. There is nothing about Mailspring that is simple and easy. If you’d like to help things along, consider helping us fix some of the bugs, especially urgent ones. That will free up Ben to implement these larger features, such as the Calendar.
Thanks for clarification. Mailspring is the tool I greatly prefer over others on Linux. Also, the calendar is not really a major issue, I just use an OS-spanning calendar besides which does its task well. I was just wondering on the time it takes for the Mailspring calendar to get done, but you have given good reasons - good luck for continuing this marvelous project.
Yeah, I am in the same spot with needing a Calendar that works well in Linux. But, for what it’s worth, Ben wants this feature too. 
Thanks for your understanding!
I think the need for a combination email and calendar system on Linux has become more urgent recently. Evolution is bloated and not a great solution for anyone not using Gnome. Up until now Thunderbird has been great with the third party Google Provider for TB extension, but the latest version broke calendar invites through email and introduced a bug where dismissing notifications removes all invited parties. For this reason, I am stuck unable to accept calendar invites that are sent to any address outside of @gmail.
I won’t go into any more details but basically I’m desperately looking for a good replacement. Are there any ways that we, as a community, can help push this along? I didn’t realize there was a preview to this feature yet so I guess I’ll try that next and provide some feedback but I just wanted to ask if there might be some other way we can help.
Thanks for the explanation Jason, and I completely appreciate the sentiment!! I agree software developers are often underappreciated, especially OSS. To me, it is mind blowing that this is a one man side project at all, so a big kudos to @bengotow !! I am very impressed and excited to give it a try.
Hi @sgdavis1, we could definitely use development help! As you can see, we have quite a number of bug fixes and optimizations that need doing, and only so much time in which to do them. Every little bit helps.
Any update on any kind of calendar integration at all, either native or even syncing with Google Calendar…?
I am loving Mailspring so far but I’m not going to be able to fully migrate over to it without a way of accepting calendar events via email and setting reminders for appointments etc.
As a rule, all updates will be posted on the thread. If there are none posted, there are no updates. Your patience is appreciated. Mailspring is built and maintained by volunteers — even the core developer does this in addition to a full time job.
As a rule, asking for updates, status, or timeframe won’t hurry things along. If you want to help get a bug resolved or feature implemented quicker, here’s some things you can do, depending on your available time and skills:
And, of course, you can help just by being involved in the community: helping answer questions, triage bugs, and discuss features takes pressure off the developers, so they have time to focus on writing awesome code.
I absolutely need a calendar. When I check the preview, my calendar(s) from Google don’t load. I love this email program though!
When is calendar going to be ready and working? I am testing the preview version in the developer settings. It shows a blank calendar. Its like it is not syncing my Google calendar at all.
Hi,
I am looking at the calendar preview here. Unlike @dahauss, I can see my calendar subscriptions, but I can’t:
Just like other people here, I am looking for a basic calendar support which consists in
Thanks
Hello,
Thanks for the great email client in linux.
We need really a calendar that just works in linux environnement. Our company has taken the PRO version to support your effort, so please make the calendar works ASAP.
Regards
Is there a beta version I can use to help with tests?
Love mailspring and would like to adopt it for work, using calendar with CalDav integration.
The goal is to have appointments sync w/mobile, along with personal stuff fm gmail.
Hv some technical knowledge and could help dig errors on logs and debug stuff.
If that helps, would love to contribute.
All the best.
Almost forgot: using on elementary OS 5.1
Can we have a calendar support feature pleas. this is of utmost importance.
I have been comparing several Windows mail clients and so far I like Mailspring best, BUT, I need to be able to accept Google calendar invites at least and this doesn’t seem to work at present. I still need to go to the Gmail web client.
I’d be very happy to be a beta tester for this. Otherwise I will move on to the next client on my list. So far I have tried:
I have a couple of others to look at, I think currently MailSpring is my favourite but I do need the calendar integration.
Cheers
please keep posting your findings… i’m in the same boat wanting close integration between gmail and gcal… i’m a dev so i’m tempted to do the unthinkable and start my own project 
=> https://github.com/Beej126/GmailZero
any update on this? would really be helpful to have a calendar feature on the stable build