Mail not being received from Zoho Campaign

Mail not being received from Zoho Campaign

Hi

I sent a campaign out yesterday to our club membership, of which only 50% have been opened.  Previously I felt this could be an issue of engagement, however it turns out many people are not receiving the emails. 

I can attest to it, as even I didn't receive the email from my own campaign (my personal address being a Yahoo account which never previously had issues receiving campaigns).

We have asked people to check their spam etc, but it seems it cannot be explained this way.
The campaign indicates no bounce-backs, simply that people are apparently receiving and not opening, which is not the case for all.

Could you please explain this?  Or is there a way to re-send the campaign to those who 'haven't opened the email'?

Sharleen.