It would be great if Outlook sync'd your email signature across multiple devices so that you only have to set or update it once.

Enable an option to display declined meetings in teh calendar (in settings). Often initially one is not available for a meeting, but then due to changes of schedule might be able to join, but since that meeting is not displayed in calendar, simply forgets about that. I found that option very helpful in Google mail that we used up to now in the company.

In Microsoft Outlook 2016, when we forward\reply\reply all to the email with attachments, the attachments are not available and we have to attach them manually. An option to reply all to the email with all the attachments included would be more productive in Microsoft Outlook 2016 as that option is not available as of now.

I would like the option to send meetings requests with BCC, CC so all information about all invitees is not shared with everyone that is invited

Also, Outlook calendar entries need BCC, CC – without showing these and need to extend them to Skype as well as Microsoft Teams Meetings.

Sometimes the owner of a meeting (or, more often, meeting series) is on vacation or changes jobs; it would be nice if they could assign ownership of an instance (for vacation) or the full series (for job changes) to someone else. Also provide an option to create a meeting on someone's behalf without being included in the meeting.

Outlook needs a unified Inbox similar to the Outlook for iOS app. For those of us with multiple email accounts it would be very convenient to have all emails arrive in one inbox; perhaps color-coded to show which account they were delivered to.

I'd prefer to keep the history of my past tasks and whereabouts, so I would like an option to "remove only future meetings in this series"

Provide a feature to cancel a recurring meeting with future meetings only and don't lose the history on the Calendar.

Many people use the "Accept - Do Not Send a Response" option thinking that they are recording their attendance on the calendar event but not sending an email that will flood the organizer's inbox. This option should be updated to reflect the way most users interpret it, or there should be another option that serves this purpose.

I find that I cannot change the color of agenda items or calendar items for my email accounts in Microsoft Outlook. I use various Android apps on my tablet and phone, that allow me to show Agenda items and Calendar items. If I use gmail, I can easily select a color, whereas with Outlook accounts I cannot change the color to suit my preferences. Also provide an option or feature to set different events with different colors in Calendar as well as in Categories in Microsoft Outlook 2016.

Please make it possible to synchronize Gmail contacts and calendar without 3rd party apps.
Also, It should let you synchronize the google calendar and the contacts, but store it in the Gmail account not locally.

Add 'Acknowledged' and 'Thanks' buttons to emails that will tell the sender you have seen/appreciate their email, without having to send another, thereby reducing email traffic.

Option to allow calendar items to have multiple reminders in Outlook 2016. As an example, it would be great to be able to set one reminder for two days before and another for one hour before. Also setting multiple reminders and in increment of 5 minutes interval would be an added benefit. Also an option to allow reminders to be changed when right clicking appointments in Outlook calendar.

Also as for the agenda, provide an option to set a different ringtone / alarm clock from the default one.

Allow multiple months in the to-do bar like in Outlook 2010. Restricting it to a single month defeats the purpose of having it there.

Add additional Calendars to the To-Do Bar.

Outlook 2016 only allows you to view the events located in your default calendar in your to-do bar. Having a feature to add multiple calendars overlapped in the to-do bar calendar would provide a better understanding of my daily schedule. One particular calendar I'd like to add to the to-do bar viewing is a shared calendar so using only categorize to filter is not a viable option.

Having a feature like this would allow for an easier way to view your schedule at a glance in the to-do bar.

You should be able to (under tracking) easily email or reach out to those who have not responded to an outlook invite to a meeting request. The only way I see it can be done now, is to hand extract those individuals and resend a new meeting request.