How do I block a sender on my iMac? I keep getting spam texts.

Never reply to a spammer, any response will be recognized as a possible phish and soon web links by the thousands will surface

I do know in Canada that carriers and the government regulators are working to correct the problems, since then the volume of fraudulent callers and spam messages has decreased

From the txt message>i (info)>Hide Alerts:

or Add them to your contacts and block

How to block a contact in Messages for Mac

1. Open Messages on your Mac.
2. Click on Messages in the Menu bar, then choose preferences.
3. Click on the Accounts tab.
4. Under your iMessage account, hit the Blocked tab.
5. Tap the Add button (looks like a '+').
6. Select which contact you would like to block.

Sep 28, 2016

How to block FaceTime calls and iMessages on the Mac | iMore

kayel wrote:

It’s text messages.

Same answer, really. Contact the SMS carrier, in this case.

Same for spam telephone calls, too.

With the latest iOS, it’s possible to disable notifications from all but known senders. Muting notifications is available in macOS. Blocking in iOS, too. But blocking doesn’t work, when the spammers vary the sending number, and the same as they do with email spam senders...

Related discussions with some details:

Blocking / Reporting Spam Texts - Apple Community

Can't block sms with no number - Apple Community

Log some feedback with the folks at Apple, too:

Product Feedback - Apple

Blocking a spam sender in an email client does little good. Spammers have found ways to bypass client blocks by chnaging the email's sender on the fly. Log into your email provider's webmail page and see if they have a server level block available to you.

Send one SMS reply with the following content and case:

STOP.

This is supposed to be honored, but time will tell how effective it is. I have had about five text msgs over the last few years where this worked everytime.

Don't you think I know that? Certainly true for email.

People can see that their sent text message is delivered, so they already know it is a valid target. The use of "STOP" worked for me with several unwanted text messages, and those messages never arrived again.