Add a error message on send buttton of email client popup

[Siddharth4]

Hi,

I have a requirement to add a error message on email client popup, that comes up when fulfillers try to send the mail from ServiceNow,

As per the ServiceNow property the outbound email size should not exceed 25 MB. So I want to add a error message on the send button of email client popup so that if fulfiller try to send the attachment of size greater then 25 MB the confirmation message pops up.

I found this article but It's not working for me - 

https://www.servicenow.com/community/developer-forum/send-button-on-email-client/m-p/1546013/page/1

Thanks

[Ankur Bawiskar]

@Siddharth4 

unless UI script triggers you won't know

[Siddharth4]

@Ankur Bawiskar  Can you please help me with the steps to get the confirmation message on the send button on email client?