Also new to Outlook 2016 for Mac is support for delivery and read (opened) receipts when sending messages. Microsoft notes, though, that email recipients can choose to decline to send read receipts.

We have POP3 / IMAP email set up. You probably don't have both, at least not on the same machine. Which is actually being used?

Does the user have multiple machines/devices where the email is received? If you are using IMAP on all/any email clients, then the sent email should be viewable via a webmail portal and you could confirm that the sent items do actually still exist (i.e. Weren't inadvertently deleted). If you can see message in the Sent Items folder via webmail, then either the IMAP settings are only configured to synchronize from a limited timeframe, or there is some sort of filter applied on the Sent Items folder in Outlook. Check the IMAP settings and make sure it is configured to sync all messages and not just 3 months back or something. Otherwise, you'll need to find and fix the Outlook filter (probably just reset it to default).

If you are using POP3, each machine/device will have its own unique Sent Items folder and you would need to determine if it is an issue with sent items being on one machine vs. If they changed machines, is the email on the old machine and/or did the PST file get transferred to the new machine? You could try mounting a copy of the PST on a different machine to confirm if the Sent Items from 2016 are still there. If you can confirm they are actually still in the PST, then you have a filter issue (like above). In either event, you need to determine if the 2016 Sent Items didn't accidentally get deleted. If they didn't, then check Outlook view filter settings for the Sent Items folder.

RedWingFan wrote: You probably don't have both, at least not on the same machine. Which is actually being used? Mw2 mod menu for mac on steam. Does the user have multiple machines/devices where the email is received?

If you are using IMAP on all/any email clients, then the sent email should be viewable via a webmail portal and you could confirm that the sent items do actually still exist (i.e. Weren't inadvertently deleted). If you can see message in the Sent Items folder via webmail, then either the IMAP settings are only configured to synchronize from a limited timeframe, or there is some sort of filter applied on the Sent Items folder in Outlook. Check the IMAP settings and make sure it is configured to sync all messages and not just 3 months back or something.

Otherwise, you'll need to find and fix the Outlook filter (probably just reset it to default). If you are using POP3, each machine/device will have its own unique Sent Items folder and you would need to determine if it is an issue with sent items being on one machine vs. If they changed machines, is the email on the old machine and/or did the PST file get transferred to the new machine? You could try mounting a copy of the PST on a different machine to confirm if the Sent Items from 2016 are still there. If you can confirm they are actually still in the PST, then you have a filter issue (like above). In either event, you need to determine if the 2016 Sent Items didn't accidentally get deleted. If they didn't, then check Outlook view filter settings for the Sent Items folder.Agreed, most likely a filter applied.