Hi @Samiunnisa Shaik , welcome.
Typically we see folks having trouble getting an invitation email to an Atlassian Cloud site if their account was created in Atlassian Cloud before their email was set up (in the case of new employees) or if there was some temporary problem with the company's mail server.
When our mail service receives these errors from a recipient mail server, we'll temporarily pause sending more messages until the error has been cleared out. If you are able to provide the email address that seems to be having the problem, I can check our mail delivery service to see if there's an issue (and then will edit the email address out of your message). You are also free to put a private support ticket through on the support portal as Fabienne mentioned, although it may take a little longer for the issue to be investigated through the support portal due to our expected wait times.
Daniel | Atlassian Community Support
Hi All! We’re excited to share the launch of an announcement banner that lets Jira site administrators communicate directly to their users across their Jira Cloud instance. ...
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