Signature documents are reaching junk/spam since last few days

It has been noticed that since last few days (weeks), any documents for signature triggered through echo sign, is reaching to junk to most of the clients (irrespective of what email they are using gmail, yahoo, hotmail). We have to chase up making call for signature. Even reminders reaching junk/spam. Something has changed since last few days and as it is affecting gmail, yahoo, hotmail etc., looking like not our or any other individual's fault. Need urgent attention.