@peopleinside Thank you very much for your response. I have changed to prod. mode and cleared cache.
However, when I tried again, I get the same error. But this time with an error page.
In the image below.
The version of PHP am using is 7.4
And UVdesk stable V1.1.0
@savelam Can you try with PHP 8.0 or better 8.1 or, if is a problem I suggest to wait here for a developer reply. This can take some time, some hours or some days.
@peopleinside Thanks. I will try with php8 and get back.
@savelam Hi, any news about this issue: switch to PHP 8.1 resolve the issue?
Waiting your feedback 
Have a nice week end!
@peopleinside Thanks very much for your continued support. I have tried with php8.1 but still experiencing the same issue.
Address in mailbox given [email] does not comply with RFC 2822, 3.6.2.
@savelam thank you for your reply!
Just to be sure: email address that you set in uvdesk have some special characters like a full stop or the domain after the @ is a subdomain?
@peopleinside No please, there were no special characters before or after the @ sign.
@savelam understood. Sorry I have no idea so... we need a reply from developers.
Share your email id which you using to create a ticket.
we will check to create a ticket from your email id.
@komal-sharma said in RFC 2822, 3.6.2. compliance error when sending a ticket:
Share your email id which you using to create a ticket.
we will check to create a ticket from your email id.
You can share privately by using a ticket: https://support.uvdesk.com/en/customer/create-ticket/
Insert email adress on a forum can generate spam to this email address
@peopleinside I have sent the ticket using the support link.
Thanks.
@savelam great, please keep this topic updated so when a solution will be available, we can mark the topic as solved.
@peopleinside Sure I will keep you updated. Thanks.
@peopleinside I have received a response from the support them. We are still on it. I will update you when everything is sorted out.
Thanks.
@savelam great, thanks 
peopleinside 29 May 2022, 15:03
@peopleinside the issue was resolved by commenting out the code block in the function, assertValidAddress() located inside
vendor/swiftmailer/swiftmailer/lib/classes/Swift/Mime/Headers/MailboxHeader.php
I do not know if what I did is the right way to go about it but it works for me and I wish to share it with the group.
Here is the screenshot of the code block in the function that was commented out.
Can you tell us which email service are you using & also which UVDesk version are you using?
@vipin the UVDesk version is v1.1.0 and am using office365 email service.
The error is saying that the email address you are providing does not comply with the RFC standards. Make sure your email address variable is not blank.
The fully RFC 822 compliant regex is inefficient and obscure for validate email address because of its length. Fortunately, RFC 822 was superseded twice and the current specification for email addresses is RFC 5322. RFC 5322 leads to a regex that can be understood if studied for a few minutes and is efficient enough for actual use.
If you use HTML5, use this code:
<input type="email" name="email" required placeholder="Enter a valid email address">
Mail your query us at support@uvdesk.com. Our team will help you.
@peopleinside Thank you very much for your response. I have changed to prod. mode and cleared cache.
However, when I tried again, I get the same error. But this time with an error page.
In the image below.
The version of PHP am using is 7.4
And UVdesk stable V1.1.0