Error with mass texting

[mscroggs2017]

I am getting the following error when trying to send large amounts of email to text through my server. "Communication with SMS gateway failed. Did you configure mail transport in lib/config.js? Error message: 'Invalid greeting. response=421 Fork failed: 421 Fork failed'"

I have set my exim smtp defaults to allow max connections per the advise of the internet and am still getting this error.

Any ideas on how to fix/circumvent this issue?