Emails from my Website are not coming through

The most common cause for this problem is that the emails are not formatted correctly, header-wise.   Websites should not be impersonating the sending domain of users that use a webform to submit a request. For example, if customer John@acustomer.local logs into a website www.vendorB.com run by the 3rd party hosting company www.theisp.com and submits a webform, the email  generated by the webform must not come FROM: John@acustomer.local.   Why Not ?   John probably has (or should have) an SPF record for his domain acustomer.local. that lists ONLY the mail server(s) for his domain as authorized senders on behalf of his domain. When the 3rd party hosting company server tries to send the email as if it came from  John@acustomer.local the mail servers that get the email will think that the message is fake (spam) since the message did not come from the proper mail server (mail.acustomer.local) - it came from a 3rd party website at theisp.com. Since many thousands of customers may send web form emails each day, from many thousands of new domains, the mail server and dns configurations cannot be changed each time (in advance) of an email beings sent!    How to fix the problem:   The changes needed are simple. The web form needs to generate a From: field in the email reporting the email to be FROM the webserver, with a Reply-To address set to the person that should get replies, and a return path to a bounces mailbox that is monitored.   For example, the email headers should be generated like this:   From: www@www.vendorB.com Reply-To: customerservice@vendorB.com Return-Path: vendorB-bounces@it_support.com   Vendor B should be setup with an email config that has a person in sales/marketing monitoring and responding immediately to the customerservice@vendorB.com mailbox and a support person watching the bounces@vendorB.com at least every 24 hours or so.   What will happen is that when John@acustomer.local submits the form, since the From: address will match the vendorB.com domain (and the website IP address should be added to the SPF record for vendorB.com too) the recipient domains will be able to correctly identify the proper source of the email as the web form service.When (if) a person in customer support goes to reply to the message, the Reply-to address will be used, not the From address, which means the reply will work (assuming the customer put in his correct email address).   The only time the bounces@ inbox should ever get an email is if the regular mailbox for customer service cannot accept the message (common problem: over quota!) For this reason as shown above its often wise to have the bounces email on a different domain than the from: in case the entire from domain (vendorB.com in this case) is having email routing problems or a DNS outage.