This behavior is by design. When Outlook 2011 for Mac downloads data from the server, Outlook first downloads the email headers and message bodies, and then Outlook downloads the attachments for each folder in batches of 20. During this time, the status displays Inbox: Downloading Attachments x/20. You use Microsoft Outlook 2016 for Mac or Outlook for Mac 2011 to connect to a mailbox on a Microsoft Exchange server. When you send an email message that contains a large attachment, you receive the following error messages in Outlook for Mac. Take the following steps to fix the issue: Mark all messages with attachments in Inbox as read and clear Folder Cache (Right-click the folder Properties Empty Folder Cache), then start downloading items again. Inbox should contain as few items as possible, 3000-4000 is the recommended maximum for Outlook for Mac. Step 4: Click the OK button to exit this dialog box. Then Microsoft Outlook 2013 or 2016 will warn you automatically if you may forget attachments. For example, you enter the text of “please check attachments”, “view attachments”, etc. In your message body, but do not insert attachments in the Attachment field.When clicking the Send button, a warning dialog box will pop out to say. Open attachments directly without asking by saving all attachments firstly in Outlook. Normally we can save attachments from one email with activating the Attachment Tools and applying the Save All Attachments feature in Outlook. But, what if saving attachments from multiple emails, or from the whole mail folder in Outlook? Try Kutools for.
Outlook on the Web (what used to be called OWA) has a useful feature that checks an email you’re about to send, and if it contains words that indicate that there should be a file attached to the message, will warn you that nothing has been attached. It’s very nice, and it’s something we’ve all done once or twice or a few hundred times over the years, so I certainly appreciate the warning.
Included in the warning is that tick box to tell Exchange “Don’t show me this message again.” Obviously that tick box exists to cater to what is surely a small number of people who frequently mention words like “attachment” or “attached” without actually attaching anything to the email message, and therefore don’t want to be nagged about it all the time. But of course, it also means that normal people are going to tick that box by accident, and then complain when “that warning that usually appears didn’t show up and I accidentally sent an email without an attachment!”
Fortunately, the setting is controlled in the message configuration for the mailbox as an attribute named CheckForForgottenAttachments, which can be checked by running Get-MailboxMessageConfiguration.
There are the 10 methods you could try to fix Outlook not working on mac or outlook 2016 for Mac Crashes Constantly error.
#1. Run MS Office Update
It is safe to say when Microsoft software is operated on Mac, they will glitch or cause some problems. It does not occur very often but when it does it can really become the annoyance. Especially in the case of Outlook 2016, Outlook Not Working On Mac Mojave or Outlook 2016 For Mac Crashes Constantly are regularly popping.
Recently with the latest update, Microsoft has fixed this crash problem. So we recommend you to update by opening the MS Office, and navigate to “Help” and “Check for Updates.”
Outlook 2010 Attachment Options
Also, Microsoft Office 2016 only supports OS Yosemite X10.10 or higher. The lower version like Mavericks X 10.9 and older version are not compatible with MS Outlook 2016.
#2. For Mac Database rebuild MS Office 2016.
One of the easiest and fastest ways to fix Outlook errors is to rebuild the office database also referred to as creating a new identity. In Outlook 2011 it can be done manually, but in Outlook 2016 it was removed as Mac claimed rebuild should be done automatically. If the Outlook database encounters an error then only it prompts you to rebuild the database. It is a quick way to fix errors but many times it just does not work if the corruption is serious and if it is not executed properly there is a risk of losing all your emails.
Note: If you are using MS Exchange then it recommended to synchronize all the data and create a backup because while creating a new profile all the files will be deleted.
Follow these steps to rebuild your MS Office 2016 database:
1. Open application folder and locate MS Outlook.
2. Now hold “Ctrl+Click on MS Outlook”, and now select “Show Package Contents”
3. From “Content” > “SharedSupport” > “Outlook Profile Manager”
4. Now tap on “+” to add a new profile.
5. Now lastly click on the “Option” and set as “Default”
#3. Outlook 2016 crashes while sending emails
If your MS Office 2016 is constantly freezing or crashing while sending emails or Outlook not working on Mac Mojave, Catalina, High Sierra while sending emails. You can create a new identical Outlook account and delete the previous one. It is a simple but effective method to fix it. Below are the steps you need to follow:
1. On the home page of Outlook, go the “Tools” and click on “Accounts”
2. A Wizard will start as “Set up my Inbox”
3. Now select “Add Account”, then select the account type either “Exchange or Office 365”. After that add your email accounts.
4. Type account info and then click on “Add Account”
5. Now tap on “Configure automatically”
microsoft office#4. Outlook 2016 for Mac crashes constantly on Startup
If your Office 2016 is constantly crashing while opening, you need to delete Outlook 2011 files from the installed location or just move them from the installed location of Office 2016. This will not affect your files in any way. To do so follow the steps:

1. Go to the “Spotlight” and search for the “Terminal”
2. In the terminal type: “default delete com.microsoft.Outlook”.
3. After that type “Killall cfprefsd”, doing so will kill all the cached.
4. Now relaunch the Outlook.
#5. Exchange errors with MS Outlook 2016

If you facing some trouble while adding Exchange account to MS Outlook 2016 that means you are probably using a different version of Exchange which is not compatible with the Office 2016. Below are the examples of the errors:
Office 2016 for Mac is only compatible with the Exchange 2010 SP2 or above only. So if you are using the older version you should definitely update it asap.
#6. MS Outlook 2016 crashes or hangs while Importing PST files
Usually, when large PST files are importing from outlook Mac, they will either hang or crash. There it is advised to compress the PST file if its size is in Gbs before importing. To compress the PST file follow these steps:
1. Go to the “Account Settings” and then “Data files”
2. After that click on “Compacting”
3. If you don’t want to compress, you can use any third-party app to split PST files.
Note: If you still could not fix Outlook not working on mac or outlook 2016 for Mac Crashes constantly error. You should contact Microsoft Office Support.
If you want to export your PST files from Mac to Windows read this blog or simply try this Premium Tool.
Conclusion
These were the six easy ways to fix Outlook not working on mac or outlook 2016 for Mac Crashes constantly error. One last piece of advice I would like to give is to always to keep the backup of your files as you never know when and how your file could get corrupt.