Bulk sending capabilities

I run a small security business in InfoSec and wanted to use mail-in-a-box to send phishing emails… I was wondering what it’s capabilities were and if it could handle larger clients that receive 5000+ emails a day from us…

If this isn’t tested what would be the predicted bottlenecks? Server will be on a $20 digital ocean so I think that will be ok… But the actual rate of emails being sent concerns me. The phishing platform we use sends about 1 a second via smtp settings so just thought I’d check before jumping in.

What would happen if I chucked 20000+ emails in? If it errors on a few, how would I trace this? Is this just a no-no, or you think it could in theory.

Appreaciate any input you have on this. I realise it’s a bit of a different question but require a self hosted SMTP server for security reasons and thought mail-in-a-box was a good starting point.