some emails not received

Today i have noticed on “flamingo” widget 2 old messages from clients – I have never seen on my email. These messages were never show in inbound messages on my Thunderbird, nor in spam box – so only flamingo widget saved these messages.

Have any idea why CF7 doesn’t send some messages (these were from gmail and yahoo)?

when I’m testing contact form 7 on my website – everything is OK and every test messages show in emailbox (I’m using to tests different email accounts (as sender) and many devices such as pc/smartphone etc..) So after all-successfuly test I even don’t expect any troubles.