I have created a managed package in a developer edition org that contains send email button. When I install the package in another test org(dev edition), everything works fine. But , when I install the same managed package in Sandbox every thing works perfect except send email button. I am badly stuck in it. What could be the issue I am unable to debug
Please check your email deliverability settings.
To send an email on sandbox, change the setting to "All Emails"
Here is the reference article: