Verizon acquired AOL (2015) and Yahoo! (2017) and successfully merged their email infrastructures in 2019. The AOL and Yahoo! brand names and domains continue to be used with consumers and they use the same spam filtering technology.

Best practices 

• Opt-in permission: Subscribers that opt-in are more likely to engage with your email and less likely to complain, which can improve your chances of reaching the inbox. Do not purchase email lists or engage in list harvesting techniques.
• Complaints: Ensure you are signed up for their Complaint Feedback Loop program and suppress subscribers that complain. 

• This program helps you to:
• Understand what email subscribers think of your messages
• Take corrective action to minimize the complaints
• Improve your sending reputation
• Check your complaint rate and strive to keep it below 0.2% for an IP address. IPs with a complaint rate higher than 0.2% are more likely to have mail sent to the spam folder. 

• IP segmentation: Segmenting your email traffic flows by IP can help improve deliverability as well as make it easier to troubleshoot deliverability problems. Most senders segment marketing and transactional email, but you should determine what works best for your business.
• Authentication: Make sure you are properly authenticating your email with SPF, DKIM, and DMARC. These authentication standards help you establish a consistent domain reputation and prevent spoofing of your domain.
• Reverse DNS: Publish reverse DNS (PTR) records for your IPs. Do not use generic names such as ".in-addr.arpa". Create something meaningful to your business that reflects your domain name.
• Engagement: Ensure you have good list hygiene practices and remove inactive subscribers regularly. Identify when subscribers typically stop engaging with your email and send them a win-back email. If subscribers continue to be unengaged with your email, consider sending them a re-confirmation email before adding them to your suppression list. 

• Segmentation: Target your subscribers with relevant content based on demographics and other attributes such as past purchase history, buying frequency, and industry. This helps increase engagement which can improve inbox placement.
• Verizon Media caches images using a proxy server, so location based targeting may need to be adjusted.  Image caching also can distort (undercount) open rate data. 

• Review your SMTP error codes frequently: Ask your ESP or email administrator for access to the files or reports that contain this information. The error codes can provide insights into potential problems, so reviewing them on a regular basis can help you identify small problems before they become big problems. 

• Retry sending for 4XX bounces, but look for signs of throttling. If your IP is being throttled, reduce your volume.
• Retry sending if the servers are temporarily busy.
• Do not retry sending email with a 5XX code until you have identified and fixed the problem.
• Unknown users with a 5XX code should be suppressed after one bounce. 

• Onboarding new IP addresses or domains: Return Path recommends warming up new IPs and domains over time to build your sending reputation. Mismanaging or rushing the warming process can cause email to go to the spam folder and adversely affect your business. 

• To start, send only five messages per connection (open a connection, send five messages, close the connection, then repeat). Increase the number of messages per connection over time.
• Monitor the SMTP codes for signs of throttling. If you receive an error indicating throttling, adjust your connection and throughput settings and slow down the volume until the throttling messages subside. 
• Message limitations: Yahoo! Mail accounts can send and receive emails up to 25 MB, so most marketing email will have no issues with size. 
• Unsubscribe: Honor all unsubscribe requests within 24 hours. Sending email to people that have unsubscribed can harm your sending reputation because they are more likely to mark futures messages as spam. 

• Implement the list-unsubscribe email header using the one-click unsubscribe method.
• RFC 8058