During past month or more postings are not successfully reaching subscribers who use gmail or google apps. The error reported is:

host aspmx.l.google.com[74.125.142.26] said:
   550-5.7.1 [192.135.176.103      11] Our system has detected that this
   message is 550-5.7.1 not RFC 2822 compliant. To reduce the amount of spam
   sent to Gmail, 550-5.7.1 this message has been blocked. Please review 550
   5.7.1 RFC 2822 specifications for more information. pp8si350824icb.106 -
   gsmtp (in reply to end of DATA command)

Mail has been delivered to these subscribers without incident for years  in some cases. No other recipients get a similar error.

Has anybody else been encountering this problem and have some suggestions?

Google has a reference page: https://support.google.com/mail/answer/81126#authentication 

Thanks,
Barry Krawchuk
ITS