[Koha] Email delivery pending

[Shankar Reddy Kolle]

Dear Sir/madam
Greetings.
I have migrated Koha version 19.05 to Koha 22.05.08 in Ubuntu 22.04.
An in-built SMTP server is enabled to send emails to the patron.
The system sends the welcome email after new patron registration
but it does not send the chekins and checkout email.
it is showing the notice is pending.
Please help me to figure it out.

Thank you in advance.

-- 
Best regards
Dr. Shankar Reddy Kolle
Deputy Librarian
Prof. Ram Dayal Munda Central Library
Indira Gandhi National Tribal University (Central University),
Lalpur,  Amarkantak, Anuppur Dist, Madhya Pradesh -484887, India
Phone No 09742749018
https://www.scopus.com/authid/detail.uri?authorId=56963777200
https://www.researchgate.net/profile/Shankar_Reddy_Kolle
https://scholar.google.co.in/citations?user=Msk5hT8AAAAJ&hl=en