If you use SMTP services like Mailjet or Amazon then your email could be sent from multiple possible IP addresses. An easy way to identifiy these ip addresses is by looking at the SPF record.
This is easily done using googles dig tool https://toolbox.googleapps.com/apps/dig/#TXT/pinakin.me.uk
You will see an SPF record like this.
"v=spf1 include:spf.myukcloud.com -all"
If you use linux then use the collowing
dig TXT spf.myukcloud.com +short| grep ‘v=spf1’
if you use windows
C:>nslookup -type=TXT spf.myukcloud.com | find "v=spf1"