dial tcp i/o timeout

[gml-sec]

I want to scan the smtp fingerprint information of the specified domain name list, but I found that if there are too many domain names in the input file, almost all the results will report the following error:

"error":"dial tcp xxx.xxx.xxx.xxx:25: i/o timeout"

It seems that the number of IPs scanned at a time cannot exceed 50, otherwise such an error will be reported. By the way, This is the command I used:

zgrab2 -f mx.txt -o res.txt smtp --send-helo --helo-domain gmail.com

Is there any way to solve this problem?