Emails not being received by some recipients

[#1]

Hi, I'm a little concerned as to wheter my emails are working as intended, I say this as although I know emails to family and my work email are received without issue, I've had emails sent to Garmin support, and Silverstone experience customer services not get received by the relvet persons. yet within a day or two of sending from my work O365 Exchange account they've received and replied.

Are you able to do a mailtrace for emails If I provide time and date of sending?

Emails that don't get received have been sent from both Thunderbird (Win10) and Apple Mail (macOS)

[#2]

Interesting post as over on BT community, serveral customers are seeing that emails sent using an email client such as mac mail using an @btinternet email address to send to an @icloud.com or @me.com email recepient,  are not being received by them.

They are being shown as sent with no error message being received.

However if one uses the bt webmail then everything is working normaly. 

This appears to be an intermittant thing when using a web mail client,  as although it went wrong a few weeks ago, it worked yesterday but today has stopped again.

Wonder if cause is releated .

[#3]

That's interesting as my Dad has been having similar issues with his BTinternet emails.. He's using the Microsoft Mail client on Win10 though.

[#4]

You can follow the BT Community link here unsure if you need to be a member to view though.

https://community.bt.com/t5/Email/BT-email-addresses-not-being-received-in-Apple-ICloud-email/m-p/20...