I use Thunderbird on Linux Mint with several email accounts. Recently, every email to one organisation has bounced. Receiver advises he has "recently enabled Sender Policy Framework (SPF) security. Emails are getting blocked because the sending email server does not have SPF enabled or is configured incorrectly." All is OK if I log into gmail and send from gmail, SPF problem seems to be introduced by T-bird. I discovered an article suggesting it might be caused by SPAM filtering on gmail but I cannot see how to change that if it needs changing. Current solution is to send from a different (non gmail) account on T-bird. Any helpful suggestions appreciated, thanks

Gordon