auto response issues with ISPs

[Anonymous]

We are having issues with people registering for our webinars not receiving our auto response email. Under lead history, it states that the lead received the auto response email from us, but they don't have it in their spam folder either.  Some leads are using @gmail or @yahoo email addresses. Can anyone shed light on this? is this because their isp blocks it? thanks. 
 

[Anonymous]

Sounds like you are getting filtered at the ISP level or ending up in the junk/spam folder. 

Have you got your basic deliverability items in place like SPF and DKIM? 
https://community.marketo.com/MarketoArticle?id=kA050000000KyrDCAS

You may also want to run through Josh Hill's guide to Email Reputation Management: 
http://www.marketingrockstarguides.com/wp-content/uploads/2012/10/Email-Reputation-Management_108.pdf

Lastly if your volume is under 100K a month and you only send to opt-in leads, talk to Marketo Support about getting on the Trusted IP range, which can help your deliverability.