Imac not sending iMessage but can receive messages

What version of macOS are you running? What model iMac?

Did Messages work properly previously?

Have you tried restarting your iMac? Sometimes that is enough to resolve unusual issues like this.

Open the Messages app preferences, click on the 'iMessage' preferences tab, then click on the 'Sign Out' button, then sign back in to see if it helps solve the problem.

Boot into Safe Mode and test Messages from there. Then reboot normally and test again.

NOTE: Safe Mode boot can take up to 10 minutes as it's doing some system cache cleaning, volume verifying and directory repairing.

My iMac was not sending photos/images via iMessages. It would progress to about 90% and then it would sit there and eventually fail. I have tried some other solutions but none of them worked. I deleted the messages folder from the library. It did not help. Signed in and out of the iMessages app, signed out of my phone. Nothing.

This solution helped and worked EdCr, not sure why but I found that file in keychain access and deleted. Restarted the iMac, sent a test and no problems file sent completely.

strange solution not sure what it is but thanks.

Good clue, likely corrupt Keychain entry, thanks. :)

This key deletion worked for me also. Would NEVER have found this solution, so many thanks! Evidently key was added 10/28/2018... exactly the time my iMessage stopped allowing me to send on my MacBook Air!

I have tired this 2 times and each time com.apple.facetime:registrationV1 returns and I still can't send messages. iMessages worked just fine before I installed Catalina. At first, I thought maybe something was wrong with my 2018 MacBook Air but I just had a new hard drive installed in my 27" iMac, so this is a clean install of Catalina on a new hard drive, have not migrated anything over from time machine. iMessages work fine on my iPhone with most recent updates installed. Aside from Catalina, the only thing I have installed on this new hard drive is Adobe Reader, Adobe Creative Cloud Photoshop, and Office 365 Home.

My point being, there is something wrong with Catalina! Somewhere deep down inside of Catalina there is a little gnome that is throwing a wrench in iMessages.

I am having no trouble sending or receiving iMessages. But all of a sudden I cannot send SMS texts - and yesterday, all my SMS texts came into my mail. I'm running Catalina on a brand new iMac, but have not upgraded to this latest version. I'm going to do that now. I followed your instructions re: keychain access with no good result.

My original post long ago took another direction right off the bat. I have no trouble sending or receiving iMessages on my phone or my iMac. It is the messages (SMS) that I receive from friends who don't have iPhones that don't show up on my iMac, nor can I write to them from the Messages app. They come into my phone just fine. This didn't happen until I bought my new iMac last fall. It is up-to-date, running Catalina. There must be some setting I'm missing. Suggestions?

EdCr I have absolutely NO idea how anyone would know to do such a thing, but it did fix the issue. Thank You!

This is amazing! Thank you it works! I've been so frustrated not being able to send a message!

Thank you so much!