Mail problem

I suggest starting with this article: Troubleshoot email problems in Mail on Mac - Apple Support

Then rebuilding your Mail app's mailboxes: Rebuild mailboxes in Mail on Mac - Apple Support

If neither of the above helps, then I suggest that you run an EtreCheck report, and optionally, post it here if you need assistance with interpreting its results.

Ref: Using EtreCheck to Troubleshoot Potential… - Apple Community

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.

You can save us asking dozens of questions by submitting a report from this App for us to look at…

EtreCheck is a FREE simple little diagnostic tool to display the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to help people help you with your Mac. It will not display any personal info.

https://www.etrecheck.com/

Pastebin is a good place to paste the whole report if you capture the URL while there…

https://pastebin.com/

Whew, they've changed pastebin & made it harder, but after pasting in, click Create new paste button, then Embed button, then copy the URL...

<script src="https://pastebin.com/embed_js/KuvnghqA"></script>

The important part is...

https://pastebin.com/embed_js/KuvnghqA

Workable but harder for me to work with...the Note tool on the bottom of this editor's toolbar, as shown in the image, to copy and paste the output from EtreCheck. In a Reply before you click post, look for this to add longer texts...

Hi, I have the same problem. I have closed down the mac and rebooted, I cannot do the 2 steps you suggest as Mail will not open to enable me to do this. I have downloaded the EtreCheck but am not sure how to copy and what to copy from the report. My mac is 2009 edition and is on OS X El Capitan (i have not been able to update it), so a beloved old relic, any help would be gratefully received!

Same problem. Mac 2009, love it, looks like new, but e mail does not open. Generally slow. Not able to update.

Apple store suggests to buy a new one. Could it be saved?

hi, I tried running in safe mode and the same thing happened, I have run the etrecheck and here it is(attached report) ! Do you think it is a case of obsolesce???

Thanks for your help!