OK – it now seems that the updated Contact Form DB 2.8.16 works properly. Phew! (Thanks, Michael)
It has been somewhat confusing because of an unhelpful time-lag in delivering mail, but I’ve run some mail delivery tests using various combinations of Contact Form 7 3.9.3 with Contact Form DB (various versions). The results are as follows:
1) Original installation of CF7 3.9.3 with CFDB 2.8.13 (Never updated)
Direct mail (TO:) works properly – mail delivered
Additional Headers (BCC:) works properly – mail delivered
2) Updated installation of CF7 3.9.3 with CFDB 2.8.15
Direct mail (TO:) does not work – NO mail delivered
Additional Headers (BCC:) does not work – NO mail delivered
3) Contact Form DB DELETED completely (leaving only CF7 3.9.3)
Direct mail (TO:) works properly – mail delivered
Additional Headers (BCC:) works properly – mail delivered
4) Contact Form 7 3.9.3 with reinstalled CFDB 2.8.16
Direct mail (TO:) works properly – mail delivered
Additional Headers (BCC:) works properly – mail delivered
Glad to have got there in the end ?? and apologies to Michael (developer) for any confusion which might have been caused along the way!