The Watchtower under discussion did mention delivering mail to a church. Additionally, it referenced, but did not quote, Matt. 5: 45, which says that God makes it rain upon the good and the bad. So, there is no proscription against delivering mail to a church
The following address the clerk selling tobacco issue.
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km 2/74 p. 4 Harmonizing Our Employment with ‘Love of Neighbor’ ***By comparison there may be a Christian who is simply an employee in an establishment that sells tobacco incidentally and who has no voice or control in what is sold. For example, an employee in a restaurant may be called upon by a customer to sell him a cigar which the management stocks. Or, one may be working in a food market; groceries and meat are the principal products sold, but the owners stock tobacco as an incidental item. The Christian employee may be expected to collect money for items that are sold, including the tobacco. Personal conscience would have to dictate what he or she in this situation could and should do as to handling tobacco products to this extent. He may prefer to ask the employer to relieve him of any handling of these objectionable materials. Unless a serious issue would arise, such employee would not be restricted from serving as a pioneer, an elder or a ministerial servant in the congregation