I somewhat agree with you here. Junk mail is not great, and I think that's what they are talking about. If someone has asked to be contacted, such as by filling out a contact card then that is another story. Sometimes if you visit a church they will give you a contact form, and it will have a check box that says "I would like a visit" etc.So other than the obvious signs, which I tend to agree with overall what I'm getting here is that being friendly and thanking you for coming are bad things? Being friendly would be one of the good signs for me.
Yeah its overkill.To me, if you go to a church once, and they blow up your phone for the next 3 months saying what a pleasure it is to have you and how you should come back, it might be a bit of a red flag.
There is an industry, however, which caters to religious organizations. This industry is probably what drives a lot of these kinds of emails. There is church support software, church mailing designers, etc. It could simply be that whoever is behind the emails lacks sense. On the other hand they might do it in spite of the annoyance in order to occasionally get a new member out of it. Perhaps if they email 300 visitors one will come back because of the email spam?