In Django 1.8+, the template’s render method takes a dictionary for the context parameter. Support for passing a Context instance is deprecated, and gives an error in Django 1.10+.
In your case, just use a regular dict instead of a Context instance:
message = get_template('email_forms/direct_donation_form_email.html').render(ctx)
You may prefer to use the render_to_string shortcut:
from django.template.loader import render_to_string
message = render_to_string('email_forms/direct_donation_form_email.html', ctx)
If you were using RequestContext instead of Context, then you would pass the request to these methods as well so that the context processors run.
message = get_template('email_forms/direct_donation_form_email.html').render(ctx, request=request)
message = render_to_string('email_forms/direct_donation_form_email.html', ctx, request=request)