Got this response today:
Dear Americancyclo,
I am sorry for not getting back to you more quickly, but did want to answer your question about the email you received from my campaign in June. We understand your concern and take your privacy and the privacy of all voters very seriously.
According to our records we obtained your email from public records, which means that you used this email address to communicate to the Arlington County Board sometime in the last year. State law mandates that all communication with the County Board is public record and available for public examination. We did not buy or obtain your address from any vendor or other third-party source. Our volunteers manually collected the information from the public record and noted the policy area of concern to you. Rest assured your email address was NOT added to a database and will NEVER be sold or otherwise transferred to any other campaigns, groups, or entities.
I hope this information is helpful to you.
Thank you,
Erik Gutshall