How to send mail for every X months using rules?
Requirements:

Rules, Rules UI and Rules Scheduler must be installed and enabled.

Step 1) Create a new component, I named it send mail every 2 months



Step 2) Add an action of Send Mail, fill out the form, see picture below.



Step 3) Add an action (again)

This time select Schedule Component Evaluation and select your component (send mail every 2 months) 




  Note: this will re-schedule your e-mail to be sent 2 months after its
  sent for the 1st time


Step 4) For SCHEDULED VALIDATION DATE, erase everything and put +2 Months

For Identifier, put something like I did (see picture) so you know who the schedule is for.

For ACCOUNT, put account


Step 5) Create a new rule, for React on Event, select After saving a user account.

Step 6) Add an action, select Schedule Component Evaluation and select your component (send mail every 2 months)

Step 7) Click on the switch to data selection button



Step 8) Put your field in Scheduled Evaluation Date. My user date field is called From Date with a machine name of field_from_date Therefore, it's account:field-from-date

Click on Add Offset, put 2 and select Months. (This means it will send the e-mail 2 months from the from date.

For Identifier, put something like I did (see picture) so you know who the schedule is for.

ACCOUNT, put account