What services can help me bulk-send customized emails to groups instead of individuals?

Have you thought about putting all your recipients in one cell for the mail merge, separated by semicolons? That might let you include everyone while sending out individual emails with tailored messages.

To send emails to different teams, creating a distribution list for each group within your service would be ideal. However, keep in mind that for this to work correctly, everyone involved needs to be on the same email domain. If you're working with vendors, this could complicate things. If you’re using a platform like Exchange, you can set up contacts for users outside your domain to streamline this process.

I’m not very techy, but I understand that using nested Outlook mail groups could work for this situation. You can create groups for specific departments or vendor companies, like a ‘paper goods’ group that includes all relevant companies and their users. This way, if someone leaves, you only need to update their email once in their respective group, and it’ll be reflected in all combined group emails.

If you're using Google Sheets, there's a helpful add-on called MailMerge for Gmail by digitalinspiration.com. It's designed to help with sending bulk personalized emails which might suit your needs.

You're spot on about Mailchimp and similar platforms; they're not designed for the kind of group email you need. Those tools mainly focus on individual recipients and don’t support ongoing threaded conversations within groups. For your requirement of sending bulk emails while maintaining individual conversations, you're looking for a specialized email service or CRM solution that better fits business communications rather than marketing. You might want to explore options like specialized email services that allow for group mailing with tailored CC lists and continued thread tracking.